pts said..."So maybe cut 60 HZ and below for the mains, and set the subs at 80 HZ? Then there’s still a little play between the two. I see how not drawing such a hard line with the frequencies could help not create a hole in the audio."
Setting the subs low pass at 80 hz will not relieve the mains from also playing in the subs bass frequency range. The inclusion of a high pass filter of say 100 hz will only let the mains produce frequencies at 100 hz and higher,thus relieving the sub and mains from reproducing the same frequency... With less overlap... the better the in room bass response.