I'm willing to design it here, open source & proofed on EEVblog (in a new dedicated thread). However, I will be designing the schematic and PCB in Protel 99se. I know it's old, but I legitimately own it, know how to use it's in and outs, and, I'll provide all source files, gerbers, and documentation... Everything will be 100% manual routed...
The PCB will have the USB interface with optional isolated DC-DC converter for the dac and analog section, or, an AC input with regulators. It will be the choice of which components you stuff. The I2S Data lines will be opto-isolated
There will be line level output on RCA, with maybe an optional balanced output, or, 8 channels out instead. I don't know which yet.
Stereo input will be there as well.
You will be able to set a fixed optional +Xdb gain resistor on the output as the output driver amp will have a +/-12v supply with the headroom.
If there are any additional takers, let me know now as it will help me decide whether to go or not....
If there are any special additional considerations, let me know as well.