I appreciate the waterfall graphs. Owie.
I really like what Jakewash said. In my room, I really like to run my M60's with a 60Hz crossover point, because I have a nasty null in the room at 70Hz. Using the mains at *somewhat* lower frequencies really helps smooth out the bass in the room. Now, with two subs, you're going to have more options than I do, but the same principle holds - having sources of LFE at different points in the room MIGHT make a difference if your amp can handle it. With M80's, you probably have quite a lot of useful response between 40Hz and 60Hz and it is entirely possible that the material BELOW 40Hz is what was giving your Denon trouble in that scene.
So, I'd experiment a bit.
