Yeah, 6.1 has a rear center channel.

It's largely been replaced by 7.1 (surround back left and right channels), as apparently the brain perceives sounds coming directly behind you (as it would in 6.1) in a strange way, so having two channels in the back, but on either side of your head, is a better way to do this.

And before you ask - in 7.1 setups, the regular surround channels aren't meant to be behind you so much as to your sides, and maybe slightly behind you. I think that's what you're supposed to do for 5.1 as well, but everyone I know with a 5.1 setup puts the surround channels way in the back.

As a sidenote, my roommate has a 7.1 setup, which is awesome and all, but the receiver will not accept audio through HDMI. Therefore, we have to use digital optical ... which can't carry a 7.1 signal (or lossless surround audio). Thankfully, DTS-HD MA 6.1 is fed through as DTS-ES 6.1, so I was able to get the full 6.1 experience with Philosopher's Stone (spread across two channels instead of one, of course).

I wanna know who the hell thought it'd be a good idea to make a 7.1 receiver that can't decode HDMI audio...