I really only have 6.1 set up using the 770 since there are no 7.1 source materials just yet, only created signals from the receivers.

I went to the 770 because it is the same size as the 755, and gives me 2 extra channels. So I could use if the 6th/7th channels, which I use the two rear speakers I have running in parallel at 4ohms for the 6th channel. As for the extra channel, I am thinking about biamping my center speaker which will take some work on my part since it is not normally biampable.

So, if you front speakers are biampable, then you could use the extra two channels of the 770 for that and still have a 5.1 set up for home theater. Of course, you could purchase the new 2 channel outlaw AMD later if you want to add the back speakers down the line. Lots of options.

Also, one thing to consider, the 770 runs all speakers even when I am listening in stereo mode (ie, there is a slight signal hiss in the center and surrounds when you listen closely). This is why some "audiophiles" buy separate two channel amps for the fronts and then another 3, 4, or 5 channel amp for the rest of the home theater setup.