Sounds like your couch is right where the bass frequencies are cancelling. Maybe you could get a subwoofer and put it at center, give it a crossover around 80-100 hz or so (or whatever ends up sounding right so that the cancelling lower frequencies are handled by the sub instead of the L/R channels), and let your L/R speakers do the punching, and your sub could handle everything lower. That should take care of the cancellation at the sweet-spot.
Dunno how you feel about subs, but you don't necessarily need them for sub-freqs. Just having one speaker handle the low end you do intend to put out will be better for the cancellation issues that arise when the longer wavelengths are coming out of two speakers.
I'm sure you already know all this, but I'm bored and I'm working very hard at getting you to talk to me, as you haven't since you've been back and I think you're mad!
