Well, today I re-tested with test tones, and the situation is different what I assumed. After pink noise calibration (at 5 db above the rest of the channels), It seems have much higher response from 25-50 hz than at 60 and 80 hz (the crossover point). It's actually a little high and boomy in the 30-45 range. So I think what's actually happening is that movies have a lot of impact in low frequencies (30-50 hz) during test scenes, whereas typical music is punchier from 50-80hz, excactly where my response is fainter.

Unfortunately, for now I really have no placement options at all, and no ability to move the sub.

[Just thought I'd add this addendum. I called my subwoofer company (Definitive), and they suggested that I raise the 950 crossover across the board to 100hz. They were concerned that the internal crossover in the sub (set at 100, and not bypassable) might be conflicting with the crossover in the 950, creating a cascade effect.

The end result is a much flatter response at 60 and 80 hz (which makes sense), though still with a big dip at 80hz (which at this point I'm pretty sure is a standing wave). Now, music sounds pretty great with the sub set about 2-3 db high using pink noise, which is about right for movies, too.

One interesting thing, though--using the sub with my main speakers full range (bypass) does AWFUL things to the sound. There's a huge peak at 40hz, and a total suckout of frequencies at 50hz. There must be a phase difference at certain frequencies that both the sub and the mains reproduce. The mains by themselves in bypass sound great, though a little boomy (they're apparently creating some standing waves of their own).]

Hope this helps someone!