I just bought my DENON 3805 with a 5.1 Allantic Technology 5.1 4200 speaker system MADE IN HEAVEN ok here goes, 6.1 is for one speaker in the rear 7.1 is for 2 speakers in the rear. I added 2 old Cerwin Vega speakers on the back wall set the amp to 7.1. and the sound is so involving and dynimac the two rear speakers really make a difference, Also did you have your 3805 callibrated using the mic? VERY IMPORTANT The calibration E.Q.s and balances all you speakers in closing On the face plate on the left side it shows your imput feed mono, stereo, and 5.1. great feature The only problem is it has so many features and took me days to figure everything out great choice also I own A DENON 2910 d,v,d player awsome picture quality good day stewart