Part of the confusion, I think, is that for a 5.1 MUSIC system the surrounds *are* supposed to go at the back, roughly where the rears go in a 7.1 system.

For a movie system, though, the surrounds go exactly where Randy said.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8