On the surface, it's just another set of modifications, right? Another way to sell CD-63s, eh? I suppose that a cynic could look at it that way, but - after hearing the 'K.I. Signature' - the cynic would have to recant. Moreover, the lateral thinker rather than the cynic would recognise in the Marantz CD-63II K.I. Signature CD player (to give this machine its full name) a set of opportunities rare in audio which can help to convey vividly the meaning of the term 'upgrade'. That's because the K.I. Signature, the third variant, makes the CD-63 uniquely positioned to do so.

Traditionally, models dubbed 'Signature' tend to be hot-rodded versions of products which are upmarket from the outset. Ones which come to mind include a couple of Acoustic Energy speakers, some Grado cartridges of yore and the like. But, for the most part, hi-fi manufacturers do not tend to run numerous concurrent versions; it's confusing and messy. So, invariably, when a product undergoes extensive modification, it becomes a replacement for the model on which it was based. With the latest version of the CD-63, however, the consumer can - like the car buyer - choose according to price and desire within a same model 'family'. And Marantz has priced them far enough apart to ensure that they're not mutually exclusive.

Think about it. If you want a car, any car, the odds are that it's available in myriad forms, to suit both your budget and your expectations according to social and/or driving needs. A Peugeot 106? 1.1 or 1.4 litre engines, diesel, three- or five-door, sporty or plain. A Ford Fiesta? You'd need a whole magazine to list the options. In hi-fi, it's take it or leave it. But Marantz has given us the plain vanilla CD-63 (now Mk II, that is), then the CD-63SE with uprated chassis and improved components, and now the Ken Ishiwata Signature version. As all three are currently available, it affords the retailer another unique opportunities beyond being able to offer three variants of the same model to the customer: it enables the shop to perform vivid A/B/C demonstrations which are beyond reproach.

Imagine, if you will, going into a shop to buy a CD player for £500 or under, and - instead of being offered three wildly different, mutually exclusive models from three non-sympathetic manufacturers - the retailer shows you a trio of models identical but for details which enhance the performance. At extra cost, of course. Prices? The basic CD-63 can be found for around £270, the '63SE for £350. The new K.I. Signature? £500. A nice point spread, so to speak, guaranteed to space the models sufficiently to avoid confusion. And provided that the retailer has three copies of the same CD, you can feed all three versions of the Marantz into the same line-level preamp or integrated and switch from one to the other for perfect comparisons. How so? Since they all work from the same remote control, setting up synchronised playback is a breeze.

Fundamentally, a CD-63 is a slim-line budget player jam-packed with every facility expected of a CD player, plus remote volume control (great if you have a pre-amp or integrated lacking said convenience item). It uses Philips' CDM12.3 three-beam laser assembly with digital servo-drive (DSD), a single-bit converter and Hyper Dynamic Amp Modules (HDAM) to reduce noise in the analogue output section. The latter devices are probably the secret to the CD-63's supremacy in the entry-level arena. What Ken Ishiwata has added to the SE's recipe to justify the Signature tag are a new, over-sized ultra-low-impedance toroidal transformer, a completely copper-plated anti-vibration chassisand improved copper versions of Marantz's HDAMs. To give you some idea of what the K.I. Signature HDAMs do, they improve on the 80V m/sec slew rate of cheap'n'nasty op amps to typically 15V m/sec.

Only two external details identify the K.I. Signature: the flashy name plate on the front and large copper-coloured areas visible underneath. It's this which is particularly Ishiwata-esque, harking back to the high-end Marantz CD players with which he's been involved, including the CD-12/DA-12 which started the ball rolling. The overkill power supply, matched components and greater resistance to vibration are also Ishiwata trademarks, so the K.I. Signature labelling is no mere conceit. (It should also be known that, belatedly, Marantz Europe has recognised Ken's deserved pan-European celebrity status and its market value. And putting a designer's name on a product must be a first of some sort for a Japanese electronics firm, even one that's Dutch-owned.)

Given that I keep a '63SE as my budget reference and a bunch of duplicated CD titles for such comparisons, I was able to A/B myself into oblivion. Alas, the results were more difficult to confirm because the gains were of the most subtle sort, and certainly not as gross as the difference between a standard '63 and the 'SE. It's a situation which, ironically, provides us with another unique opportunity: an audition consisting of the standard CD-63II versus CD-63SE versus K.I. Signature provides painful proof of 'The Law of Diminishing Returns'.

Consistently and repeatedly, the SE versions of Marantz CD players have bettered their bog-standard progenitors with superior dynamic capability, better retrieval of detail and greater coherence. For a fee typically 30 percent dearer, Marantz provides a higher level of performance for those who could justify it. Can't hear the difference? Then don't buy an SE. Can't afford an SE? Then buy the standard model, because it's still pretty damned good.

Only this time it's not quite so clear. For one thing, the price difference between the Signature and the SE is £150, or nearly double the difference between the stock '63 and the SE. And the £80 it costs to go from stock '63 to '63SE yields more than the £150 which takes you from SE to Signature. And unless you consider yourself to be somewhat golden-eared, you'll probably go for the savings.

Even so, anyone who hear the differences between an 'SE and a Signature needs a course in Remedial Hearing. The gains may be subtle, but they're not what you could deride as 'barely audible'. If you can't hear them, fine - you've saved £150 which you should spend on having your ears syringed by a professional. The differences, while not exactly night and day, will be apparent even through the kind of systems you'd expect to host a £500-or-less CD player. Or, to put it another way, you don't have to arrange for an audition via Krell amps and WATT/Puppies.

It's all a matter of presentation. One local Marantz dealer tells me that he finds the Marantz '63s grow more 'in your face' as they acquire added status. And it's true that the various CD-63s are not laid-back or shy. On the other hand, they're graceful enough to survive comparison with far dearer players, so the 'in your face' aspect relates more to physical presentation rather than sonic aggression. Or, to put it another way, the images are more forward through the Marantzes, almost in front of the line of the speakers, when compared with the spatial presentation of the competition. Rotels, for example, seem far more genteel because of this.

But since a CD-63SE is so coherent, commanding and generally hard-to-fault, what your extra £150 for Ken Ishiwata's stamp actually buy? Perhaps the only consistent complaint one can muster about these extremely affordable players is that they can show traces of coarseness, minute amounts of sibilance and the occasional bit of shout; with the Signature, such displays of errant behaviour grow less frequent.

Indeed, the one recorded passage which I A/B'd continuously for a good half-hour was Keb' Mo's 'Am I Wrong', which seems to upset CD players the way heavily modulated tracks on LPs could (physically) aggravate a stylus. There's so much energy in the recording - a mix of powerful dynamics, scary transients and over-burdened upper frequencies - that it has a tendency to embarrass systems with the facility of a deliberately nasty test disc. Hell, one of the reasons I love the track so much is the element of surprise it contains; you never know when a system's going to fall apart. Through the K.I. Signature, the risks were lowered to barely negligible levels, while the 'SE consistently turned raw.

What makes A/B'ing the SE and the Signature so difficult are the similarities; you'd think that their common traits would make it easier to hear the differences. Not so. Both produce an identically sized and shaped soundstage, with the stage width, depth and height varying not a centimeter, the images reside in identical planes, the bass extension is interchangeable, the output levels match closely enough to tax my trusty Tandy SPL meter. But a few weeks of to'ing and fro'ing turned up other subtle variations which might not manifest themselves in a quickie demo in a store: The K.I.'s bass is richer but better-controlled, despite identical estension. The dynamic range seems wider, with low-level sounds enjoying greater security. The midband is warmer and less clinical. And similar soundstages or not, the K.I. offers greater stage depth when the recording demands it.

But there's a I can't avoid. Even though it's possible to ascribe the above differences, it's much harder placing a value on them in this context. C'mon guys: if we were talking about two pre-amps at three and four grand respectively, and the dearer one demonstrated just one area of supremacy, we would probably justify it. At this price point, however, £150 is a huge percentage of the cost to accommodate so glibly. And it's arguable that just going from the standard cables which come free with the CD-63SE to some prime interconnect for £50 would yield improvements (if not exactly the same ones) of a similar degree.

Insofar as the existence of three versions of the same CD player has provided hi-fi retailers with a foolproof way of silencing the kind of spouses who try to embarrass their partners with, 'Gee, dear, I can't hear a difference', it also shows how undeniably is the basic machine. And, as a result, how much we have to pay for incremental improvements. The K.I. Signature is, equally undeniably, the more refined and 'mature' player and the one I prefer across the board, but I can't avoid telling you that the cheaper CD-63SE is too damned good for it's own - and Marantz's - sake.