This could be a really nice room if you put the TV on the short couch wall and moved the long couch parallel with box B. I took a quick look at the the dimensions. Your current layout throws away a lot of performance potential. You are sitting too far and too narrow a ratio for your mains to seating location. Sitting on the back wall is not a good idea. Not only for bass but it really destroys any chance in hitting an optimal layout -which is doable in this space.