Sound is excellent with two minor exceptions: 1) right M80 seems slightly crippled by rear projection being muffled by ventilation duct on bottom wall, to correct this I would need to slide everything to the left including placement of center speaker,
A trick I used in an old room, which might save the substantial work you are talking about, is to put a panel/screen behind the speaker (or all the way across the wall, or behind both speakers, whatever works for you). You can pick your price really, simple to exotic to match the room. Allows the air return to work fine, but gives you a point of reflection that you can control and deaden as you like.
Just as an example:
screens or
oriental I built my own using closet doors from home depot, and you can make whatever size and design you like. Just an idea before you fire up the wrecking ball.
