Quite the room you have going there. Given that it's about 25X13 (approx.) I would definately go with something a bit bigger. I don't have much experience with the Arch. series of speakers, but I am not sure how they would do in such a large environment.
If it were me, I would def. go with the amps, and get some 60's or 80's plus a 500 or 600 sub (or any other brand sub) to get the most sound, in the space. QS8's will be fine...but there is so much possibility with that room.
Maybe others will chime in, but if it were me, and my train of though, I would just go with M80's all around, and a couple of 500's. But, since you are looking to 'hide' it all, and not consume too much space...I guess the Arch. series would be an OK choice as well.
Good luck with the decision.
