Hmmm...
That is odd, so you will play the same video feed in each room? with one video source? In other words you want 15 speakers and 3 subs and 1 receiver with 1 cable box and 3 tv's?
If I understood that correctly, off the top of my head, Im thinking...
2-UPA500's- $400 eachhttp://shop.emotiva.com/collections/amplifiers/products/upa500
1-http://www.accessories4less.com/make-a-store/item/MARSR5004/Marantz-SR5004-90w-X-7ch-Home-Theater-Surround-Receiver/1.html
Would be the easiest way, then you could power all 3 at the same time if you like...
As far as useing speaker selectors, Im thinking it will be a horrow show and not much cheaper for what you end up with....
This way you just run rca's from your preouts to your 2 aux amplifiers with a splitter on each one, and then split the sub preout to each rooms powered subwoofer...
The hard part is going to be splitting the video signal if you are using hdmi...