I know that Roon has no access to an output if Plexamp is used and/or the output is not released within the Plexamp app.
So it is possible to use Roon and Plexamp on different outputs (maybe Plexamp at HAT Toslink and Roon at RPi4 USB) at the same time? Has anyone tried this?
You can have multiple DACs connected via USB and each can receive the stream as a group so I imagine this would work if you can set one to use the HAT and other use USB. But one app just might take over the ALSA pipeline so maybe not.
I just tested successfully from one ropieee endpoint. Plexamp playing through one USB (a generic usb spdif) and Roon playing through the other (a Dacmagic 100).