I connected a REL subwoofer (or, as they call it, a "sub-bass" system) to my Stereomour. REL recommends connecting to the speaker output terminals of the Stereomour, so I did that. So my speaker output terminals had wires going to the REL subwoofer, as well as wires going to my 2-way speakers.
The REL is powered, and has a crossover.
I think there are multiple solutions; this one worked well for me. Good luck!
Mary
DIY 2-ways (TAD TD-2002, AE TD15M), Stereomour 45
Fostex TH-500RP, S.E.X. 2.1
Eros Phono