Listener:
Don't get too worried yet, this usually ends up being a connection issue.
First thing to check: Make sure you have the sub RCA cable connected to the sub pre-out connection on the back of the Denon. There are a couple of other RCA outs on the back that look very similar and are easy to confuse.
Second: Check the "gain" knob on the back of the 350. You want it 1/3 or 1/2 of the way to full volume to start with. (at that setting, your receiver shouldn't need to be anywhere near +12, but don't worry about correcting that until you have more bass coming out of the 350)
Third: Crossovers and Receiver Speaker Setup. The most common settings here are to cross over the fronts and center at 60 or 80. (I believe more people do 60). In your speaker configuration, set your front & center speakers to small, and set the sub to "LFE + Mains" (you can change this back to just LFE later if you like, but for purposes of making sure things are working, I'd start here).
Finally, if none of these change the output from the sub, perform a simple test to ensure you are getting sound from the sub only. Do this by entering the speaker setup menu and going into channel level. Choose "Manual" and then go to the subwoofer channel. Make sure that you are hearing a low (probably loud if still set at +12) rumble from the 350. If you do not, then you have either a bad speaker or still have a connection/configuration problem. If you try all of the above and still don't have strong bass during this step, something more serious is wrong.
Try this and let us know if it improves, if not, others will probably offer additional ideas.
Jason
