Hi,
it maybe that I am missing something in Audacity, but I also tried Ardour, and also couldn’t get it to work.
But I have never worked with these programs before, so maybe I got it wrong.
And maybe there is no Combo-port on the Librem15rev2, but I think in this post there was a layout sketch which seemed to suggest this:
(But unfortnately the “specs” figure doesn’t load anymore. I think this figure is very important and instructive, but I didn’t print it at the time, so maybe one could bring it up again, please?)