I have two subwoofers because:
a) I have a large room (20X23 with high vaulted ceilings), and
b) I have openings to other rooms at each corner. Not a great room to trap the bass. Lots of "leakage".

I have the subwoofers set up next to each speaker but that is probably not the best set up. Better to have each subwoofer 90 degrees out from each other.

I think I will probaly get the SMS1 bass room correction unit in a year or so. That unit will should smooth out the bass response. I am running DefTec BP 20's BP2000 CLR, BPVX and BP2's from the 990 and 770o.