Having the back wall separate from the seating will actually improve the rear soundstage. You're lucky if your set up permits you to do this. My couch is slammed right up against the rear wall, so placement of the rear speakers was tricky and makes the effect a lot less, well, effective. To compensate, and disperse the rear surround speakers, I point them up towards the ceiling so I get reflected sound that more closely replicates sound coming from above and behind me. Your set-up is far superior, it seems, to most here, since most of us do not have dedicated home theater rooms with multiple rows of seating and an enclosed "box" environment with many options for placing speakers. It's gonna sound great!
