Foghorn,
I run a 6.1 system, and my current rear speaker is a crappy little JVC surround (QS4 for side surrounds). I really only notice the difference is 2 scenarios...1) when watching a 6.1 channel source, i.e. Dolby Dig EX or DTS-ES, like the Lord of the Rings, and 2) when watching Dolby Surround TV using Dolby PLII or Neo:6. (I don't use any of the modes to "mix" a 5.1 signal to produce a 6.1) But the difference really is nice!! I can't wait until I get another QS4 for the rear.
PLII and Neo:6 seems to mix some of the front center and surround info into the rear surround. The modes work best on programs with good Dolby Surround mix.
As for DVD's, there's not much out there (at least, not much that I'm interested in!!) for 6.1 channel movies, except LOTR and a few others. But that back channel does make difference when mixed well.
I think the change is noticable...but I wouldn't rush into it just yet. As I've told many friends...you'll be happier with a good 5.1 system than a bad or mediocre 6.1 system.
