I have a 7.1 setup with different sorrounds and rears than mains. I use to have a 5.1 setup with full range sorrounds but thought the effect wasn't expansive enough, they were a little too low placed. I switched to higher wall mounted sorrounds and rears in the 7.1. I still use a lot of 5.1 because there is hardly any material encoded with sorround back material. I haven't heard a significant difference in sorround effect when I manually engage the matrix mode for DTS/DD when watching video. The difference is at best, very subtle. PLIIx will engage all 8 speakers automatically if you have them installed and verified by the receiver, but I haven't used that function a lot. I know 7.1 is pushed hard everywhere, and that it is touted as making a large difference in the movie experience, but IMO, it is overhyped. And I doubt it makes a difference if you go 6.1 vs 7.1. Hope you find this blurb helpful.