Chris - watch out - the guys on this forum love to spend other people's money. Before you know it, you be buying the M80's, the VP150, a pair of subwoofers, a separate amplifier, a bigger TV, a new SACD player .....
I think that you HT area is gonna be awesome. Basically, with those front speakers firing directly at the listening area, there won't be much loss in sound/volume. The open rear area might actually help to reduce some reflected sounds. With regards to the M22s and the sub, people around here tend to think that they go together like stink on a pig, and that you'll be just fine. You may benefit from moving the sub around in the listening area to see where you get the most/best response, but I wouldn't worry too much about filling that area with sound. The M22s will probably make you very happy.
That said, I think the QS8s are always gonna be a good upgrade. With the advent of 5.1/6.1 music, and better mixed DVDs with awesome surround effects, I think it is silly to chimp on these. Treat them as if they are as important as your mains. Nothing will kill the enveloping surround sound effect like wimpy surrounds. This is not to say that the QS4's are wimpy, but going whole hog on these will likely be a great investment.
Good luck.
