So, i guess overbridge will stay kind of open territory for now. However over at Elektronauts some people kind of worked out a breakoutbox based for Raspberry:
A guy in this thread ( OB for Linux (sorta ;) - General Discussion - Elektronauts ) figured out a digitakt usb driver for linux; digitakt usb audio driver on RaspberryPi · GitHub
But how to implement this into zynthianos is beyond me.
For the meantime, if i hook up the umc404 and the Digitakt i can run “alsa_out -d hw:3” (Digitakt Device number as result of “cat /proc/asound/cards”) and have as a result 5 outs i can apply zynthian effects to.