@mdsimon2 - Hi, I will give a try CamillaDSP on linux (I tried to make it run on Win with absolutely no success)
From this point:
1/. Will the tutorial from beginning of the tread work for installation on Ubuntu desktop 20.04? I am using Ubuntu since ver 12 (almost 20 years now ) and very comfortable with workflow - don't want to open another fight front except CamillaDSP by learning UB Server at the same time
2/. Does Camilla DSP resample? I have TOSLINK-USB adapter with up to 192kHz capability and USB-DAC with 386kHz capability, so they will take virtually everything without need of resampling. Will CamillaDSP push it to resample or can it just keep original sample rate (sometimes 44,1, sometimes 48 96 or 192 - all depends what source I play in WIIM Pro I have). In other words 44,1kHz in =>44,1kHz out or 192kHz in => 192kHz out etc, etc?
Thank you for answering
It will be helpful if you describe your desired signal routing as that will change the answer to your questions.
1. You can use 20.04 but it uses an older kernel which may not work well with some DACs. It sounds like you are using the desktop version which I believe by default uses Pulse Audio which might cause some issues. Overall 20.04 can work but it might require some troubleshooting on your end and there is no guarantee it will be plug and play like the process described in the tutorial.
2. CamillaDSP can resample but doesn't need to. The biggest issue is detecting rate changes. If you are using your linux computer (I take it you aren't using a RPi4?) as a source you can implement the alsa_cdsp plugin to change rates based on the file being played, see here -> https://github.com/scripple/alsa_cdsp and here -> #869 for more info.
If you are using a RPi4 in USB gadget mode you can use gaudio_ctl to switch rates, see here -> https://github.com/pavhofman/gaudio_ctl and here -> #41 for more info but you will need to use a newer kernel for this to work.
Again need more info on signal routing as if you plan on using a capture device with a different clock than your playback device like in the case of a TOSLINK to USB capture card and a USB DAC you will need to resample to bridge the clock domains. In general if you use a SPDIF input you will need some way of keeping the input sample rate constant by implementing resampling upstream of CamillaDSP. This is describe in a bit more detail in the tutorial.