Your correct, have your speakers set to small on the receiver, and a receiver crossover at 80hz. The autosetup of the Denon's will usually put your mains at large, I have 60's and still use the small setting. Also, make sure your crossover knob on the sub is either in bypass mode, or turned all the way clockwise to the highest setting, to get it out of the way of the receiver management.

take care,,,

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85