I finished the music production for beginners course a few months ago.
I’m looking an external soundcard to hook my 2 KRK-RP8s and KRK-RP10SUB to. And in general just a better quality soundcard for running Ableton. Budget up to £250-
the sub should have a crossover in it… all you should have to do is run into your sub then through it and out to your main speakers. a pair of phono to xlr then a set of xlr-xlr from sub to mains.
this is all guess work but thats how its normally done.