Hello!
Thanks for the replies!
I tried some more things:
* Putting the internal clock to S/PDIF in (or, IEC958 in) and then trying both to use the hw:Juli,1 as input, and also to connect it using zita-a2j. Using it as input, I get crashes in both JACK and QASMixer (is there any other mixer I should use for this purpose instead?), and it even hung so bad (an unkillable process) that I hade to restart the computer using the power button. Using zita-a2j, it tries to sync (instead of just spamming syncing like it did before), but it halts instantly and says it'll retry in 15 seconds (something about a too big of a timing difference, and that this usually happens after freewheeling in JACK1 or something like that).
I tried to do this with the internal clock set to S/PDIF, and I also tried de-activating the "Lock rate". No success though. I did however not try the "Lock rate"-stuff too throughly.