For my surrounds I am going to use 6 1/2 in walls due to my limited options. The problem is my walls are wood paneling and I have no access to behind the paneling. To insure the best possible sound I plan on creating an extra baffle/frame to add to the outside of the wood paneling to give it some extra stiffness. I imagine 1/2 mdf an 1/2 inch wider on each side than the grill, slightly beveled as it meets the wall to visually ease the transition, with cutcouts for the woofer and tweeter. Also stuff the wall cavity with some insulation.
Anybody have any other ideas.