Aesthetically I would like them on the rear wall as well...but not if they would not sound right back there. I am kinda in a hard place because I cant "test" different spots.

If they are on the back wall how far appart should they be and how far up the wall. The ceiling is 11' and the top of the arch is at 8' and is 13' wide. The couch will be centered on that arched openeing about 3' in front of it.