Hi Majik,
I regret you're having problems with your sub, however, I'm certain there is something very wrong or disconnected. First, if you are curious or so inclined, you could remove each woofer from the front baffle and confirm that the speaker wires are attached to each driver. This sub normally has huge output, and it might be that one woofer is disconnected. And there are no compatibility issues with the Denon's subwoofer output, so the fault seems to lie with the Sub.
Reconnect the wires if any are disconnected to either of the drivers, and try it again. Otherwise, call the toll-free number and we'll get a new amplifier off to you.
Regards,
