Osborne:

It seems like that sub should be putting out a lot more.

Excuse the biggy picture but do you have the sub connected to the SW out on your 3808 like this:


I have a SVS sub with less power in a room that has about approximately the same volume as yours. With the sub volume at 12 o'clock my Denon sets it to -2 db. Something seems wrong with your setup maybe. Just an idea...