The 755 and 770 are valuable for anyone with lower efficiency speakers, anyone who thinks they may upgrade to lower efficiency speakers later and don't want to have to replace an amp at the same time, or anyone who wants to be sure they have a good power reserve when watching movies at or near reference level. Wingnut is a good example - her Polks are about 88dB efficient (not significantly far removed from the 90dB and 91dB efficiency of the speakers in your system) and rated at 4 ohms, and she is running a 770 because the 7100 (165W at 4 ohms) didn't produce as open a sound as she felt the speakers were capable of.