I asked a similar question as my basement is 16x20 and wanted to stay with the M22's(which were shipped on monday...yahoo!!). Alan told me M22's, VP150, QS8's and EP350 at least, but leaned a bit more to the EP500.
I have gone with M22's which should arrive tomorrow, QS8's on order and my STF-3 from HSU which fills the room amazingly. I'm planning on the VP150 when I get the $$ and a buddy of mine who is a bit of an audiphile said he never regretted getting a real good center channel.
I would suggest you go with the larger center and QS8's and might be able to get more bang for the buck from an HSU, SVS, or Rocket sub.
