Sounds like your wide open to suggestions. How about an SVS PB12-Plus/2.
Maybe look at a music server. The Escient Fireball is pretty affordable.
What's your display? Maybe it's time for an upgrade there?
Yeah, display is lacking significantly in a Panasonic 1998 50" rear projection unit but I'm planning on upgrading that in a few months time with a projector - not sure which one but preferably under $1300.
I'd take awesome sound at the cost of a mediocre picture anyday, so while I would like to upgrade the display it's not a priority.
I've heard good things about the SVS sub's, but a little too late as the PW2100 is only 12 months old

. The setup is quite bass heavy at the moment what with the Monitor 11's behind, but I do like to
feel the sound too

. It would be nice if it was more dynamic/punchier though.
Perhaps it's time to get some dipole's or a rear center?