I am in the construction phase of a small theatre room. Am using BG Radia R-200 for main speakers. What modifications to the wall do you recommend to maximize the potential for these inwall speakers. Should I build in back boxes, and what volume? Bracing in areas? Sound board or insulation in the walls? Pretty open to your suggestions. Thank you.

I would build backekboxes. You'll need to check with the manuacture to see what volume they recommend. For my Klipsch in-walls, 2 to 2.5 cubic feet was suggested. I built the boxes from MDF and simply attached them on one side to a wall stud.

Same thing I'm doing. I ran out of time to do them before drywall, but it's easy enough to do. I'd follow what the manufacturer recommends though.

I agree with all of the above. get your factory recomended box size and build out of MDF. Not partical board. I did the same for my pardiagm speakers. I also mounted them in Green glue to dampen the noise going thur the wall. then sealed around the boxes with acoustic caulking.
http://i300.photobucket.com/albums/nn34/tgamble_2008/PICT0002-9.jpg
http://i300.photobucket.com/albums/nn34/tgamble_2008/PICT0001-4.jpg

I have some pictures on how I made my back boxes in the thread listed in my signature.

CJ