Sony Playstation 1.

That is the first model released.  It's the PAL version.  All original style PlayStation 1s will have the AKM DAC to my knowledge [Not sure about PSOnes (the more rounded version of the PS1 later on)].  On that model it has the nice RCA output on the unit itself.  The SCPH-1001 is the one people call the audiophile version, so I've read.  The last number only indicates region.  The only thing that should be changed is the BIOS, power supply, and video output section.  Not sure if people modify the output section after the DAC between the DAC and the RCA output to have improved sound quality.  It would differ per reversion if that's the case [Layout of the board if you are using a guide to tell you what to replace].  When I say modify the output section I mean replace the capacitors and resistors in the signal path with high quality options.

No PS1 has audiophile quality. That's just a runaway hype train.

Even if it did have good audio, it will still need a separate display to navigate. So instead of buying the upgrade parts (and the TV if you don't have one with your system yet) why not save up for a real CD Player? A decent-sounding player has a simple navigation display and a remote to boot, the only problem vs a wired controller being that it's easier to misplace around the room, and some can go for a s low as $200 (Onkyo), and Shanling has a midi-size (perfect form factor for desktop headphone systems) unit for $330. Since the transport is newer too it will serve you well for a longer time, too, and so far there seems to be no repeat yet of the CDM-4 debacle in the mid- to late-90's (when the issue of the weak mechanism were cropping up) and the NAD transports of the early 00's (where they stopped reading discs too soon, some barely a month from purchase), which hastened the release of the 'i' versions with a new transport and very mildly tweaked output section.

We can thank Stereophile for a lot of this malarkey, but John Atkinson might have nailed it when he ran his measurements:

Overall, this is a pretty poor set of measurements. I wonder, therefore, if the "magic" of the PlayStation 1's sound lies not in its technical excellence but in the fact that it smears over and disguises much of what is wrong with typical CD sound quality, to which it adds a touch of low-level compression from the linearity error. Certainly, when I recently listened to a PS1 as the source in a system comprising an inexpensive Cayin tube integrated amplifier driving Definitive Technology Mythos ST speakers, it sounded relaxed and informative in a manner I would not have expected from this measured performance.—John Atkinson

http://www.stereophile.com/content/sony-playstation-1-cd-player-measurements

Even if it *was* a credible CDP, we are talking about mass-market electronics designed to fail after 5 or so years. 1994 is now almost 20 years ago - unless your friend is a serious nutter and wraps brand new kit in bubble wrap before storing it in a dry, cool environment, I cant see that it would be worth much. On the other hand, if he has anything with 'Mark Levinson' on it, tell him I'll give him a hundred bucks, sight unseen 

Echoing, for a consumer electronic, super-low-price-on-the-used-market, the PSOne has/had the unexpected benefit of being a decent CD player, nothing more.  If your aspirations are to put it into a system on the cheap with mediocre resolution, go nuts.  Anything higher, then pay whatever market price is for a used, two-decade old gaming system.

I have several and I have compared it to the Arcam 82, NFB-3, Bifrost, Yulong D100, Nuforce HDP and many other dacs and I got to say that it came very close the all these Dacs in detail.

However, it was warmer than all of them, very analog like and had a level of tube like 3D (holographic) presentation that was freaky.  Sometimes I prefer to listen to the playstation 1 because of it's 3D like instrument separation and warmth.  Really these are amazing.