Hi, you should look into using multiple audio cards with Jack backend: How can I use multiple soundcards with JACK? | JACK Audio Connection Kit
See also my post here: How to use alsa loopback Device with jack audio backend? - #3 by Giedrius
And this may be helpful too: Problem adding additional USB Interfaces with jack_load (looks like the adapter works, but has issue in MOD-UI)
Alternatively, you could skip Jack and use arecord and aplay to pipe the audio stream through, this would work well if you don’t intend to do any effect processing. See my comment here: [Solved] No audio input going to output - #8 by Giedrius
The command I’ve shown records everything to a file and loops back to the Pisound’s output - you should be able to modify the aplay part to instead send audio through the USB card.