thanks for the comments.
using a cable to carry audio from the DAC to pulseaudio seems feasable, it's worth trying how well that works.
as pointed out, latency with bluetooth is up already anyways. only downside: it adds more components.
i found some information on the forum about using the BB-BONE-AUDI-02 overlay, but would not mind to know more about it. https://forum.bela.io/d/181-4-4-x-kernel/92 still valid? (did not read the full thread yet)
does the audio-device then have input and output channel?
what does "you wouldn't have access to the analog channels." exactly mean? analog-inputs?
the application in question (http://www.kobakant.at/DIY/?p=7575) needs analog-inputs to read some sensors.