agree with the above ...
use heavy drapes for the front wall or apply acoustic treatments ...
i also dont think it's necessary to move the center speaker away from the tv - you want the center channel as close to the display as possible.
also, try not to sit 12' away from the front wall because that's exactly half your room length and that's the crappiest location you can have. there's a 38% rule you should follow [ideally]: sit either 9.12 feet from the front wall, or from the back wall (equivalent to 14.88 feet from the front wall)
also, try to get acoustic treatments for the first reflection points.
http://www.gikacoustics.com/education.html
http://www.gikacoustics.com/room_setup.php