As Jason mentioned, Axiom might be able to provide better advice. One question I have is which speakers will be on this exterior wall, the fronts or surrounds? For surrounds you definately want to go with Q's versus in-walls, an they will mount flush on the wall.
In regards to the insulation, I don't think the W's take up much room within the wall cavity, and insulation "gives" enough that pushing it back or compressing it a little should not hurt one bit. The R value should not change for that little of an area.
I would think you would not want to seperate the insulation as this would create the ability for cool air to find a path. Compressing it back would be better.
