Amazing! I just did an Ebay search and I'll be damned. You're right. What the hell happened to all the classic Sony PCDPs?! no d-303s, no d-311s, no d-515s. Nada. And I searched the German Ebay too. Pisses me off since I never did get myself a d-303 just because I wanted to get a portable amp first but never did. You shouldn't have sold your Denon I guess
. I do remember seeing a d-515 (my personal favorite for its headphone jack) selling for a great price last summer. That's not so long ago. Maybe you just need to be patient.
I assume you are planning to use it as a transportable and not a true portable. I just paid Sony around $125 to repair the ESP and fix the tracking on my 515, and it sounded and worked great when it first came back, better than when I bought it. It was truly incredible. But after doing some fast walking with it attached to a belt clip (one of those cell phone adhesive ones) it is skipping again and/or getting all 'fuzzy' at times. I can see that owning one of these antiques is truly a high maintenance affair. I don't have the money to keep sending it back to Sony every month to keep it tuned. Maybe if I could adjust the tracking myself. I do have the service manual, but no oscilloscope.
In addition, all of my other antique players: the d-311, the d-211, the d-777 (which I never liked anyway), have broken within a few months of walking around with them (no running or anything!) as portables. The only ones that still work perfectly are the ones I never used like the d-e905 (due to my lack of an amp). I don't know what it is. Maybe just their age? As far as SQ goes though, the idea of comparing something like an (unmodded, unamped) IPod to my 515 is a joke. Not even in the same league. How it would compare to a Karma or a Vibez I don't know, or a imodded 4th gen Ipod for that matter.
You may already realize this, but I think my Chaintech AV-710 sound card has better sound (again, unamped) than any of my PCDPs. But even an SFF computer doesn't really qualify for 'transportable'. So yeah, it's a problem. And seeing the lack of players makes me even more determined not to sell any of mine. Maybe you could still buy one from the head-fi marketplace, although it looks like we have been infiltrated by some scammers there. I might be willing to sell some of my collection, but most of them (to varying degrees) have at least some kind of problem.
I wonder if this new shortage of players is due to the following dynamic. MP3 players have become more popular even among die hard audiophile head-fiers. I remember when even Duncan threw in the towel. So there was a lot of selling off of the digital disc players to the even more rabid fanatics who would actually use the things instead of just storing them. After some moderate use the players broke. They didn't seem worth fixing in most cases because you could re-buy one on Ebay for not much more than the repair costs. I hope no one threw any away for that reason. I even keep my broken d-321s just in case.
addendum: In addition to the imodded ipod, you might also consider
this. They are extremely pricey, but the Microtrack can also record (and very well!) and both would be true portables instead of just transportables.