4 years ago when only Theta processors had adjustable crossovers, I experimented with global xovers on other processors at 100Hz, 90Hz, and 80Hz and found they just didn't work well with my Dynaudio speakers in my room.

Therefore, in my processor's setup menu I set the Sub=No, Mains=large, center and surrounds=small on the processor and added an electronic xover (@60Hz) between my main towers (Dynaudio Contour 2.8) and my powered sub.

This essentially sends all bass from the small channels, plus LFE, to the main L&R channels.

This has allowed me to use the sub for both 2-channel music and HT. I hear those standup bass string plucks and HT explosions just the way I want without having to adjust the sub output constantly.

I also use a parametric EQ on the sub and sophisticated acoustic software to tune the room's bass.

The electronic xover has level controls for low-pass, high-pass, and xover frequency and uses 24dB slope Linkwitz-Riley symmetrical filters.