The back channel speakers in 7.1 do not go on the sides in the back. They go behind the listening position. Do a search.
There is no reason whatsoever to attempt an 8.1 setup at this time. There is no material, processing, or even standardized positioning.
edit:
http://www.thx.com/home/setup/speakers/back.html
There is no reason whatsoever to attempt an 8.1 setup at this time. There is no material, processing, or even standardized positioning.
edit:
http://www.thx.com/home/setup/speakers/back.html