Thank you for letting me know. So as it seems a dedicated dual-boot system would be much better rather than trying to boot up SunVox from Zynthians Debian?
If one nevertheless would atempt to do it via Jack the SunVox FAQ states this:
Start a JACK server (eg qjackctl with a GUI), switch the driver to JACK in SunVox settings. Then SunVox can be linked with other JACK-compatible applications (sound + MIDI).
To find some workable solution might be something I’ll look into later on, but ofc if anybody here has experience to share that would be helpful. Sunvox linux/pi is very polished after 18 years of continous development and would perhaps be a nice additional side-dish; possibly also compelling people invested in SunVox to buy Zynthian 5 kits for the dual-usage awesomeness added value.