Robert, both are available at similar prices in the $600-$700 area and have similar power(and also similar to your 815). The lower power rating of the 635 is due to being rated with all channels driven; if the more realistic two channel number was used, as the 801 does, there wouldn't be any significant difference in driving M60s. So, as usual, the question is what features are important to you. The 635 is a newer model and has DPLIIx(if you eventually go 7.1), while the 801 has DPLII. The 635 has the room equalization system developed by Dr. Toole's group at Harman, which you might find useful. It also has the ability to set different crossover frequencies for different groups of speakers. These are the features that in my view would make the 635 preferable.
