One way to check that your problem is not the 500 itself is to go to the channel level settings in the Denon setup menu and choose the subwoofer channel. With that channel selected, as you turn up either the gain on the subwoofer or turn up the channel level with your remote, you hear increasingly loud bass. With the 500, as you bump the volumes up, you really should be capable of shaking your walls, so if neither volume adjustment has that sort of effect, the problem may be in the sub and not in the Denon configuration.
On the other hand, if running these quick tests does produce palpable bass, then the problem will likely be solved using one of the few suggestions above, as they are the most common source of these problems.
Jason
