*pipe out audio signal directly from the DAC, and try boutique caps (Auri, VitQ 96P, and FT-3 teflon) in the signal path.
*external linear power supply for main power.
*independent analog power supply route, I will use NiCd battery power for the analog stage of the DAC chip.
*A functional control key pad so it actually looks like a CDP control (actually a re-cased controller).
*If the result is good enough, I might mount the transport to a thick chopping block and recase the circuitry..... but before that can happen it will have to beat my modified X555ES CDP.
Most of the above had been done by various DIY'ers, with the possible exception of an independent pure DC supply for the analog stage. I have already prepared the pins, it was kind of tricky, I actually had to perform the pin lifting and soldering under a 10x microscope (and the magnification helped a lot).
Pix will follow in the next a few weeks. If you have done mods to your PS1 please chip in and tell us what mod works best and what doesn't.