USB-output to USB-input?

Yep, it worked:
  • unload the current g_audio instance: sudo modprobe -r g_audio
  • load a new one with new parameters: sudo modprobe g_audio c_srate=96000 c_ssize=4 p_srate=96000 p_ssize=4 iProduct="Anything"
So I now have my audio gadget running at a rate of 96000 and 32bit. It looks like one can actually set multiple rates, but I've not tried that yet. In the meantime I have a Debian PC streaming to a RPi4 audio gadget, "hw:UAC2Gadget", which camilladsp captures from and then sends <100hz to the left channel and >5khz to the right channel of a stereo DAC output device. (i.e. just to test that it works; those filters aren't my ultimate aim!).

I need to make this happen at boot, but it is very promising so far.