I am just in the process of playing around with this very thing. I tried 2.0 and 2.1 (no 2.2 - and I think that goes for a lot of people).
I cannot tell a difference between 2.0 and 2.1. My fronts go pretty low, and my sub does not seem to go any further. Really disappointing. A $850 sub and it does not add anything to my music.
I guess I have to find something different to listen to. I know in movies it really adds to the sound. I bet my towers would not have been able to keep up with War of the Worlds like my sub did.
I stay away from DSPs. Most sound like crap. Who wants all that echo anyways? I run "straight mode" on my receiver. I tried "pure direct" but I cannot tell any difference. Like I said. Still playing.