I had seen that some time ago and read partially and forgotten where I did read it... thanks for redirecting me. Now that I have read some more, it seems that your Paul Hynes discrete regs mod has been a success. I do not see point in such a DIY unless it has something special to offer. And since those are not easily available (I assume Paul does not stock those since I understood those were left overs...), similar results you are getting are hard to duplicate. But I will continue reading, perhaps I will in the end get a new Buffalo kit and start the project.
For the case, I would be tempted to use thick raw (brushed) aluminum plate and simplistic design (or possibly a more complex design with front panel ordered from http://www.schaeffer-ag.de/index.php?id=97&L=1). Just wondering if I should first get a TC-7520 or DACmagic (or a 740c) and later start experimenting... but for me the DIY would have to be because I could make something that is worth having and not available (at all or because of cost) as a factory made product.
Have you tested a VALAB NOS DAC (preferably 2009 version) with 8 TDA1543 chips? Completely different approach, and I have not yet even had the time to seek/read what are the differences between TDA1543 and TDA1541 chips. What kind of TDA1541 based DAC is the one you have as the reference DAC?