Mark,
Hmm, I wonder whether something in your cross-over might be responsible for your *ahem* sucky frequency response. For instance, maybe you have the sub internal cross-over and the receiver cross-over both on, and set to 100 Hz, and so they reinforce unnecessarily just below 100 Hz. Frequency roll-off might not be matched. That sort of thing.
Maybe you should post some more details of your system configuration so that those more expert than I, your humble servant, might have a crack at your problem.
On the plus side, if you expand your "suck out", you might be able to replicate the famed "Bose sound" with its missing frequency response from 200 to 280 Hz between Acoustimass and satellites.
--Martin
