Hey @Kevitto, I got a chance to play with this today.
I first tried our version of Raspbian Lite for the balenaFin (available here). To get the pisound to work on this OS, I added dtoverlay=pisound to the bottom of /boot/config.txt after dtoverlay=balena-fin-updated.
I next tried the latest Raspbian Buster Lite (available here), for this I had to add dtoverlay=pisound and dtoverlay=balena-fin.
After I added these overlays the pisound-config tool reported the device information and I used speaker-test -c2 -twav -l7 to test the sound output via the 5.25mm jack on the pisound after changing the default system soundcard to pisound with the config tool.
In both cases I added the extra overlay to config.txt before installing the pisound software using curl https://blokas.io/pisound/install-pisound.sh | sh.
I hope this helps, let us know how you get on.