Thanks, Doug:

I've read that article before: Although it talks about using multiple subs to eliminate standing waves, I'm pretty sure that was not what Spiky was discussing when he said "There are problems with location of 2 subs, the sound could actually cancel out in certain parts of the room, leaving holes in your room at certain frequencies." Spiky?

Also, it doesn't address my hypothetical situation where each sub is delivering a different signal. The author specifically mentioned he was addressing a situation where all subs carried the same mono signal.

More to follow, I hope! :) Happy New Year to us all!