Potato,
I'm not sure I understand what you are saying. Building a fabric wall would bring the screen forward too much and the front seats would then sit too close.
I was suggesting a skeleton structure to hold the speakers that was very open.
The screen would sit on the drywall but I would build two towers out of 2x2s that would hold the speakers at the right height but would otherwise be totally open. These would be covered with black acoustic fabric around the whole thing. They would sit on either side of the screen. The center channel and sub would be in another open skeleton below the screen but this one would have wood on top to support the weight of someone sitting on it. The top center speaker would probably also live in a similar fabric box.
