I received my 770 last week, and after a weekend of listening, I'm very pleased with my purchase. I was using a Denon 4802r (which is now my pre-pro) which has a pretty good amp section, but the improvement with the 770 is quite significant.
My one complaint was that I was getting a pretty bad ground loop hum caused by my cable TV connection--disconnecting the coax from the wall cleared up the problem, but obviously wasn't a long term solution. I had a bit of trouble finding a ground loop isolator (as mentioned in the troubleshooting guide in the 770's manual); the few I found online were on sites I didn't find too trustworthy, and an employee at a local electronics store told me I was crazy to be looking for one...
In any case, Blue Jeans Cable offers a RF Isolation Transformer that fixed the problem for me. Since I had trouble finding one, I thought I'd give them a little free advertising and hopefully help out others who run into this problem.
http://www.bluejeanscable.com/store/rf/rfprices.htm