@snowdusk this one is for you. finally i made Mixxx work the way I wanted.First through Alsa but then the culprit of Mixxx for me was that it broadcasts/records the same output you select you can not say broadcast output 1-2 but record 3-4. So i had to pull out Jack and Carla and mess with it until it did what I wanted and configure Mixxx with Jack too ( and OBS as well). 46ms hw delay i think its acceptable.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko