The fix is mentionend at the end of the thread, it is something on Roon´s side, not Ropieee´s:
" johnRoon Labs: Support
Hello @crummwoody,
I have enabled a diagnostic feature on your account that contains an experimental fix for the issue you are seeing with the Cambridge Audio DAC. To get this fix functioning correctly on RoPieee, it will require re-flashing the RoPieee image on the micro-SD card and starting “fresh” in layman’s terms. Once you have done this, ensure that the Cambridge Audio DAC is in USB Class 2 mode, restart your Roon Core, and then connect to the device running RoPieee and see if you are able to get things to work.
-John"