Noteworthy upgrade for CD playback- how?

[stefanK]

Hello,

to start with my question: Is there a really an audible quality upgrade from a late 80's entry level CD player possible?

During the last years I have upgraded several parts of my music-system – such as speakers , amp, pick-up, tuner – to a degree that I am very pleased with. The only thing that remained the same through all the years is my CD player, a Harman Kardon HD400 (description here: http://www.harmankardon.de/specifica...D400BLK&sType=), that I bought in 1989 for about 250 EUR.
I am really satisfied with this CD player, but I always thought due to its age and low price it could be easily surpassed by a more refined player.
Thus I tried several players during the last years: Marantz CD73 (a complete flop), Playstation 1 (SCPH1002), which was just going to be hyped then, and Philips CD304MKII. None of them could compete with the soundstage and size of room, the Harman Kardon is able to display. Well, the CD304MKII came close, but only came close.
Even though not being a soldering-iron-swinger myself, I have been tracking the telling from the DIY scene about those non-oversampling DACs for quite a while, and I was quite confident, that this would be the way, in case I could find someone to build one for me. In fact there is someone, who promied to build a Doede Douma DDDAC1543 for me, but I'm not quite sure, if this will really take place.
Some weeks ago I got in contact with a german ebayer, who modifies old Philips CD600 and Marantz CD40. Those who can read german, can see his list of mods here: http://cgi.ebay.de/ws/eBayISAPI.dll?...tem=7593590735
One point is non-oversampling with 3 TDA1543 in parallel.
I tried a such a modified CD600 and compared it with my Harman Kardon HD400 and of course expected the Harman to be defeated, but: I could not tell one player from the other! The heavily modified Philips was not better in any point!

I don't think, that my hearing or my system are so limited, that the differences don't come out that clear. I assume, the Harman Kardon is not that bad despite of its age and price. My question now is: Is a quality upgrade starting from this Harman Kardon HD400 possible? If there are differences in music presentation, are they more than just a matter of taste? Which player would in your opinion be a serious upgrade? I should mention, that my budget is quite limited: I could not spent more than 200 EUR on a CD player now...

Before the DDDAC1543 was promised to be built for me (and if it ever will be built is unsure), I had thought about a Mission DAD5/DAC5, a Micromega Stage 1 or 2 or a Musical Fidelity X-ACT (external 18bit DAC). Do you think, one of these would make a noteworthy difference to my Harman? Any other suggestions?

Best regards, Stefan