Thanks that's really helpful. Can you share your ALSA config also (.asoundrc)? I'm having trouble configuring the loopback for recording the fluidsynth output.
I didn't modify any ALSA configs. The ALSA input [input.alsa(device="plughw:CARD=PRO,DEV=0",bufferize=true)] was based on output from the "arecord -L" command. The audio interface is plug & play. Good luck!