So I’ve played around with old Raspberry Models A & B running piCorePlayer with a HiFiBerry DAC. When I’ve tried plugging those old models into a USB DAC I get a glitchy output with clicks and pops. No surprise really.
The reason I say that is because I get exact the same issue running a Pi4 into a USB DAC (Geek Pulse Infinity) when running Volumio. However, if I use piCorePlayer instead (identical hardware end to end) it sounds fantastic with no glitches.
So I’m assuming Volumio is not handling the USB output in the same way as piCorePlayer but I wouldn’t have a clue how to fix it.