I think some of this depends on whether you need to have the option of separate zones or not. i.e. will it ALWAYS be okay to have the same content playing on every pair of speakers or do you need to have options?
People seem to like the Sonos stuff a lot. I can't afford it.
Parts Express has some impedance-matching panels where you send one signal to the panel and then run multiple pairs of copper from there to volume controls in various rooms. That wouldn't help with independent zones, but it would help with the cost of amplification.
Personally, I think an 8-channel ADA1000 is WAY overkill. Many of those inwall volume controls are only rated to 50W.
Whatever you do, I strongly urge you to find a solution that you can control from an iPhone, smartphone or tablet.
