I would leave things set as a 5.1 system. You need more room behind your seat for a "rear" speaker to be of any use.
Note that you still get a phantom rear image with two surround speakers, so you are missing little if anything with your setup. You may want to move that left surround speaker back a bit, but that is being a bit picky on my part. Kind of hard to look at a drawing and know for sure what lloks good in the room.
I would leave things set as a 5.1 system. You need more room behind your seat for a "rear" speaker to be of any use.
Note that you still get a phantom rear image with two surround speakers, so you are missing little if anything with your setup. You may want to move that left surround speaker back a bit, but that is being a bit picky on my part. Kind of hard to look at a drawing and know for sure what lloks good in the room.