I have a denon 1612, and I was wondering how the crossover works... Basically, I've set speakers to small, crossover at 80hz, and am not using LFE+Main setting, yet I felt the speakers were still playing the full spectrum when I did a subwoofer bass-tone sweep. I unplugged my subwoofer, and I confirmed my speakers were playing (even at 20-30hz), I plugged the subwoofer back in and still verified output through the main speakers by putting my ear close to them.
No matter what sorts of settings I try, the speakers are always being routed frequencies below whatever crossover is set. When I put the crossover at 120 or 250hz, I noticed the volume of the sounds (you know, 30hz etc.) was lower, but the speakers were clearly still active (still being routed those frequencies).
I assumed the crossover setting is supposed to mean that the main speakers aren't fed the signals below crossover; for me it seems to merely lower volume.