The key is to experiment with the crossovers and see what works best.

In my experimention, I had the exact opposite experience as you. Initially I crossed my main speakers at 80 Hz thinking, when in doubt, use a slightly higher crossover than necessary. But I subsequently experiemented with 60 Hz and found the sound integrated better, so kept it at 60 Hz. Later still, I experimented with 40 Hz and found the sound to be even better. So now my mains are crossed at 40, and my rears and center are crossed at higher frequencies.

Actually, I find I like my sub/sat setup more and more in stereo + sub mode, without the center and without the rears. For imaging, the 40 Hz is the way to go, with my stereo + sub setup, on the 950. My mains are Von Schweikert VR 4 Gen II's. It's specs say its -3dB point is 20 Hz, fwiw. BTW, I had to fiddle with phase of subwoofer when changing between 2 channel + sub, to 5 channel + sub.