The 5.1 analog connection will work for DVD videos. BUT, his processor wouldn't be applying any bass management or other processing to the multichannel inputs. The 3910 would be doing the digital to analog conversion, and he's have to set up the speaker sizes and distances in the 3910, assuming that's possible. Is there some reason he can't just use a standard digital output, coax or optical, from his Denon to his processor?
"People generally quarrel because they cannot argue." - G. K. Chesterton