I ended up going for the 763, it was just too much of a bargain to resist, I picked it up last night from Richer Sounds. First impressions after I had it all wired in and had run the auto setup were very disappointing. The sound was very bright, and my centre speaker in particular was very harsh. Whereas on my Marantz SR4200 it had a full rounded sound.
So much for the Auto setup!
I then delved around in the manual setup options for a while, Firstly turning the DRC off and then discovering that each speaker has its own graphic equaliser, after a bit of tweaking I had everything sounding much better, and a definite big step above the 4200. I still have a lot of tweaking to do to perfect the sound,(looking in the manual it seems that everything can be fiddled with in some way or other) but I'm very pleased with my purchase so far.
I did find it a bit strange that the review didn't mention the rather naff plastic volume control knob. I'm used to Metal controls with a solid quality feel to them, and the volume on the yamaha is really rather pants.