I would also say upgrade the center.. That has been the single largest improvement i have made. i went from a vp150-vp180 saying it was a night and day difference would be an understatement........

I would say get a vp160/180 and a pair of 10" subs.. I have a JBL 8" that is ok... you could probably get a pair for a couple hundred bucks.? then when you buy a "big sub" you will 1 big sub and 2 small ones.... I am running a EP600+ my JBL 8" in the family room....

If i was you, i would get the center channel at a pair of these.
http://www.amazon.com/Polk-Audio-10-Inch...2767&sr=1-2

if you have amazon prime, they are free shipping... I think the combination of a larger center plus a pair of subs for 700-900ish$ will be the largest "bang" for your buck... then you could always get the SVS PB13-ultra or a EP600/800 later and be WAY good to go!@

Also, with the pair of subs, you may decide that your m22's+ subs are just fine... which would actually save you some cash in the long run smile