"Also, we don't really crank it up loud, so I don't get too much of the sound falling apart problem"
This is not the problem for you here! Even if you listen at a "flee's level", well bellow the average listener, the problem lies in the dynamic ability and accuracy of the sound! Put your center speaker in a place where it's not coupling well at the crossover, or cross the speaker over where the speaker is "quickly" rolling off, and you'll have lower fidelity, even weak sound from the speaker (and thus the system)!
It's not necessarily a matter of whether or not you like to crank your system. If the system is going to have any chance to have any sense of power, dynamics, impact, and accuracy of response to the sound, you need to consider these things. Otherwise, you cross your fingers and hope for the best. Often times, it doesn't turn out so well, being there's so many speakers, so many settings, crossovers, phase issues, acoustical issues, fine-tuning adjustements, etc, that it all gets washed over...pulling the system down the toilet, sonically.
If I were you', I'd do this test:
Run the center speaker full range (mono, summed stereo), with a test CD that has test-tones at all the lower frequencies. Play them through the critical 63hz-100hz reigion, and see what kind of response you're getting from your center! If you're getting weak response (in relation to the rest of the frequencies, and at 1khz) at the 80hz point, or where you cross over, you've got a problem! That's where the critical bass reigion lies. You should be getting solid response down where you're crossing your speaker over, in this case, to your mains. See what you get.