Hmmm. I think I understand your plans better now.
First question, I guess, would be "why bother with 7.1 for the upstairs system ?". I'm not running a 7.1 system (yet
) but my understanding is that the primary benefit is with movies. Music and games are both 5.1 at best today AFAIK.
If I was in your shoes I would start with a pair of QS8s at the side, forget the rears for now, and re-evaluate after a couple of months.
What I can tell you is that when I had cheap surrounds I could not listen to music in 5 channels and kept switching back to "surround off". With the QS8s I leave the receiver in a surround mode pretty much all the time (usually Neo:6) and the only times I switch surround off are for situations where I would have switched it off with M2 surrounds as well.
