In the category of multi-room wireless music systems, Sonos has long been the leader, but DTS hopes to give Sonos a run for its money with the Play-Fi wireless audio standard. You can get the full rundown on Play-Fi's capabilities here; essentially, it allows you to add up to eight Play-Fi products to your existing home WiFi network (802.11g or better) and stream full-resolution stereo audio from a mobile device, Windows PC, or DLNA server to one or multiple zones.

DTS already has licensed Play-Fi to a number of high-profile audio/speaker manufacturers, including Polk--which has launched a complete line of Play-Fi-enabled products. The line features the Omni S2 tabletop speaker ($179.95), the Omni S2R rechargeable/outdoor tabletop speaker ($249.95), the Omni SB1 soundbar and wireless subwoofer combo ($699.95), the Omni P1 wireless adapter ($299.95) to add legacy components to a Play-Fi system, and the Omni A1 wireless amplifier ($399.95) to add Play-Fi functionality and power to a set of passive speakers.

Polk sent me the Omni S2 and its nearly identical twin, the S2R. The S2 is a simple-looking speaker that won't draw too much attention to itself...at least not visually. Sound quality is another story, but we'll get to that. The curvy, triangular cabinet measures just 3.92 by 3.96 by 9.06 inches, weighs about 2.75 pounds, and can sit vertically or horizontally (with rubber pads on both the bottom and side). Despite its small size and weight, its build quality feels quite solid, with an inert cabinet design and a refined finish. The speaker is available in black or white, and the front face is covered with a fabric mesh grille material. Only three buttons adorn the front face, for volume up, volume down, and play/pause. The backside includes a USB port, an auxiliary input, a DC power port, and a WiFi Setup button with a corresponding LED to assist with network connection. The S2 sports dual two-inch full-range drivers, dual 1.5- by 2.5-inch passive radiators, and a 20-watt times two (into four ohms) amplifier.

The only differences in the rechargeable/outdoor-friendly S2R are that it weighs a little more (the addition of the battery ups the weight to 3.25 pounds), it omits the fabric grille material, it adds rubber plugs to cover the ports on the backside, and it adds a WiFi antenna to help improve reception at longer distances.

The Hookup
The first step in setting up the Omni speakers is to download the Polk Omni app for iOS (v6.0 or higher) or Android (v2.2 or higher) to your mobile device--in my case, I used an iPhone 4 for setup and later downloaded the Android app to a Samsung Galaxy tablet, as well. Next, plug in the speaker, launch the app, and follow the clear instructions to add the speaker to your existing WiFi network. (You have to have a home WiFi network in place; the system cannot create its own network, but this approach means you don't need a bridge device to link to your network.) I had no trouble adding both of my review samples to my hidden, password-protected network, and the two-zone system was ready to go in just a few minutes. If you are going to set up multiple Omni speakers at once, you can send an identifying test tone to each speaker and easily rename it.

My music content came from a variety of sources. First was my iPhone 4, which is loaded primarily with compressed MP3 and AAC files. Second was the Samsung Galaxy tablet, which also includes mostly compressed music. Since Play-Fi supports DLNA, I was also able to connect to my DLNA-certified Seagate NAS drive to access my entire music collection.

I store a collection of full- and 24/96 high-resolution AIFF and FLAC files on a Windows 8 PC specifically for testing purposes, so I wanted to add that PC to the equation. Polk does not offer its own branded Omni app for Windows PCs or Windows phones; neither does DTS, for that matter. I googled "Play-Fi app for Windows" and was taken to Phorus' website (the original developers of the Play-Fi protocol) to download a Windows-friendly app for the PC. The free version of the Phorus app only allows you to stream music to one Play-Fi speaker at a time, and it will play any audio source from your PC--any music software, any streaming service, etc. However, it will also play any general Windows sound cues that occur during computer operation. You have to upgrade to the "HD App" to stream music to multiple speakers and remove generic Windows sound cues from the playback experience. That upgrade usually costs a one-time fee of $14.95, but Polk says that, when you register your Omni product through its website, you can get a code to download the full-function Windows PC app for free. For this review, I just tested the free app, and it worked perfectly fine with the Omni system. At this time, there is no Mac-compatible app, and Polk/DTS does not have one in development.

Performance
The two key performance elements for a system like this are the user experience and the sound quality. First let's talk about the user experience. Your mobile device or PC serves as both the source and control device for any Play-Fi system. The Omni app for Android and iOS has a simple, clean layout that is easy to understand and navigate (DTS offers its own free Play-Fi app that has a virtually identical layout--minus the Polk branding, of course). The Home page includes a list of all available music options: the Music section lets you access the music files stored directly on the mobile device; the Media Server section lists all DLNA-compatible servers on your network; and Internet Radio lets you browse Internet radio stations by location, favorites, genre, or name. The rest of the list features the integrated music-streaming services that Play-Fi supports; as I write this, that list includes Deezer, Pandora, KKBOX, Songza, QQMusic (Android only), and Sirius/XM (Android only). Three of those services were added during my review process, so DTS is obviously working to make more deals. The only streaming service I used was Pandora, and I had no trouble signing in to my account and streaming my favorite channels via the Omni app.

I spent a lot of time using the iOS app, and its Music interface essentially mimics the iTunes Music app in design and navigation, with options for Playlist, Artists, Songs, Album, and More running along the bottom of the screen. The Now Playing Page includes cover art (if you have it in iTunes), elapsed song time, and controls for track skip, play/pause, shuffle, and repeat. Master volume control is available via a slider along the bottom of the app screen, and the hard buttons on the speaker can give you instant control within the parameters set by the app. Overall, any regular iOS user should be immediately comfortable with the user experience. The same is true of the Android app, which shares a similar layout as the basic Music Player within Android.

Managing multiple speakers within the Play-Fi network is very simple. Press the small, orange triangle located in the bottom right corner of the app to pull up the list of all speakers currently connected to your Play-Fi network, with independent volume control for each. Through a simple touch of a button, you can instantly turn a certain speaker on or off. If another user launches their Omni app on the same network, the interface will inform them which speakers are currently in use and give them the option to override one if they want to listen to something else on a certain speaker.

At this point in time, the Android app has more functionality to set up zones (up to four). iOS support is still a fairly new addition to the Play-Fi ecosystem. With Android, you can group sets of speakers into different zones and control each zone independently. Since I only had two speakers to audition, I created two zones and found it easy to switch between them. Another exclusive to Android right now is the ability to set up two speakers in a stereo pair to function like a traditional two-channel setup.

Now let's talk performance. When I first heard a demo of the Omni S2 back at CEDIA, I was impressed by both the sound quality and dynamic ability I heard from such a small speaker. That first impression was only reinforced when I had a chance to test the S2 and S2R in my own home, with my own demo material. A single S2 was able to produce room-filling sound in most every room in my house, at least at volume levels I find pleasing. Only when I really pushed the volume in my centrally located living room, which opens into most every room and level of the house, did the S2 shows signs of strain. A dense track like Peter Gabriel's "Sky Blue" pushed the speaker's amp to start clipping and popping at high volume.

Since I also had an S2R on hand, I could fill out the sound in this larger space by simply adding the second speaker or using them in stereo. I heard no delay or synchronization problems when using both speakers simultaneously, regardless of where I put them in my house.

The S2 and S2R offer a well-balanced audio presentation for their size, with a good blend between highs, mids, and lows. No, these tiny speakers couldn't replicate either the deeper bass or the airy highs that I get from my larger (and more expensive) Aperion Allaire tabletop speaker, but they really held their own, painting the full sonic picture with most every track I feed them. I never felt like a key element was missing or overly accentuated (i.e., bright up top or boomy down low), and the midrange presence with male vocals like Tom Waits' raspy growl on "Long Way Home" had good heft and weight to them. The speakers also produced a generally wide, even soundstage; vocal quality did not shift much at all as I moved around the room, whether the speaker was placed in a horizontal or vertical position.

Play-Fi currently supports a maximum resolution of 16/48, so the higher-resolution 24/96 tracks I auditioned from Beck and the HDTracks Music Sampler (streamed from my PC) were down-sampled. I was also able to access and play 24/96 FLAC files via the Android app, but again the files were down-sampled to 16/48. Still, the S2 and S2R were able to relay the step up in resolution and recording quality of these tracks compared with compressed MP3, capturing that improved sense of space and fullness. Again, they could not provide the smooth, airy treble you'll get from better bookshelf speakers, but I was still very impressed with the quality I heard for this size and price. It's telling that Polk didn't add any DSP modes to artificially boost bass, expand the soundstage, or otherwise manipulate the sound coming from these speakers. The S2 and S2R do just fine on their own.

The Downside
With the iOS app, it took about 10 seconds on average for music playback to begin after I hit the play button, and there was a three- to six-second delay between songs. The Android app was a little faster, but there was still an obvious delay. Dave Matthews Band's album Before These Crowded Streets features a number of songs that feed into each other. Not only were there consistent gaps between the songs, but the Play-Fi system actually cut off the last three seconds of track one, "Pantala Naga Pampa," to cue up track two, "Rapunzel." This is an especially big concern for classical music fans who demand gapless playback.

I did get fast start times and gapless playback through the Windows Play-Fi PC app. And while the iOS and Android apps are limited to playback of files stored specifically within the mobile device's music folder, the Windows app will let you stream any audio source. It would be nice if there were a mention of the Phorus PC app in Polk's literature, to make it easier to find. Right now, the Omni system and Play-Fi in general put emphasis primarily on the mobile Android and iOS apps, and that probably makes sense for the mass-market audience, but I suspect the PC functionality (and the lack of Mac compatibility) will matter to a lot of our readers.

The lack of built-in Bluetooth means that "guest" devices--say, when a friend comes over--must join your home network to join the system. The wired auxiliary input is the only way to connect guest devices or play content when the network is down or out of range...and that content is limited to the connected speaker; you can't stream it around the network.

Speaking of networks, you do have to have a home WiFi network in place to use the Polk system. It does not create its own proprietary network the way a Sonos system can...and the system is therefore susceptible to the same WiFi interference issues you may experience with other devices. My WiFi system is pretty taxed and has some reliability issues, so I did get some signal drops during playback, which happens with my AirPlay systems, too. Several times upon signing in to the Omni app, it would not see the speakers on the network. I can't say for certain if that latter issue was due to my network or a Play-Fi communication problem, but I can say that any WiFi-based music system is only going to be as reliable as your personal network.

Finally, the Play-Fi system does not support playback of AIFF files from a mobile device; FLAC and WAV are supported through Android, though. I also could not play Apple Lossless files and older Apple-DRM AAC files from my iPhone.

Comparison and Competition
Clearly the main competitor to the Omni family are the Sonos wireless music products--specifically, the $199 Play:1 would be the price and size competitor to the $179 Omni S2. You can read our review of the Sonos system here. Denon's new HEOS system has a similar assortment of wireless audio products, but its lowest priced speaker costs $299. Bluesound is another maker of wireless multiroom audio products, but the Pulse tabletop speaker is $699.

Polk's sister company Definitive Technology offers a family of Play-Fi products that are targeted (both in price and performance) at the more audiophile-oriented music lover. Since all Play-Fi products will work together, regardless of manufacturer, you could actually mix and match the Polk and Definitive products (and any others that come down the pipe) based on your needs and budget in a certain listening room. At CES, Paradigm also debuted its Play-Fi lineup.

Any number of AirPlay-enabled tabletop speakers could be considered a competitor to the Omni S2, but AirPlay isn't as multi-room/multi-zone friendly as Play-Fi.

Conclusion
I feel like I'm reviewing two different things in this story: the first is a pair of Polk tabletop speakers, and the second is DTS Play-Fi as a whole, since this is our first go-round with it. The Polk Omni S2 and S2R speakers actually stand quite well on their own as very good tabletop/portable speakers in the sub-$200 category. I was thoroughly impressed with the sound quality I got from such a diminutive design, and you can connect almost any source to them directly via the auxiliary input. I even added one of them to my regular AirPlay network by connecting an Airport Express via the aux input. And the S2R makes for a great portable solution, with a rugged build and decent battery life.

Of course, a wired connection is like the cardinal sin of tabletop speakers these days, and that's where DTS Play-Fi comes into the picture. Although Play-Fi isn't brand new, it feels like it's just now coming into its own, as mainstream manufacturers like Polk, Definitive Technology, Paradigm, and others jump on board. On the plus side, Play-Fi is very easy to set up and very easy to use, whether we're talking one speaker in one room or multiple speakers in a multi-zone setup. DTS and Polk are marketing these products primarily to the mobile-device user right now; for me, the biggest kink that needs to be addressed in the iOS/Android apps is their speed and the lack of gapless playback. The Windows PC app offers the most seamless playback, the most content options, and the best file support, but it's not as multi-zone friendly as the Android app right now. Overall, I'd like to see more continuity in function and performance across all the app options, and I suspect that will come.

In the meantime, Polk's Omni S2 music system provides a great introduction to Play-Fi and a great way to bring affordable, high-quality multiroom audio to your home.

Additional Resources
• Can DTS Play-Fi Dethrone Sonos? at HomeTheaterReview.com.
• Check out our Audiophile Bookshelf and Small Speakers category page for reviews of other tabletop speaker systems.