I had a similar room setup as you and was really not very happy with the results. Putting your couch up against a wall is the biggest problem with this. This is because to get some envelopment from surround speakers you need to have at least a little bit of space behind you. The second problem with sitting against a wall is that the bass causes you problems there. I would suggest that you at least get your sofa two or three feet off of the wall so that you can get a sound-field behind you. Ideally you would want to turn the room so that your front speakers are firing into the longer dimension of the room. Now, I know that there are two big problems with you doing either of these things: 1. WAF 2. you already have your main speakers mounted in/on the walls. But, I just want you to know that your investment may not produce the results you want because of the way your room is setup.
Getting the room to look good (as far as how the furniture is laid out) and getting the speakers and seats in the right locations in the room is one of the toughest things to do in a non-dedicated room.
