Thanks for all the replies. Sorry for not responding sooner, I just got back home from Europe.
I do use Audyssey and I think it is great. I leave Dynamic EQ always ON and Dynamic Volume I keep on Day and at times may turn OFF. I have of course calibrated with Audyssey. I also have a meter that I have used in the past but I have come to trust and rely on Audyssey.
I leave the EP500 volume at mid level. My normal listening level on the Denon is 55% (absolute). After Audyssey does it's calibration, I bump up the sub level about 3db.
Also, I use a RCA cable to the sub. The RCA to 1/4 Phone adapter that plugs into the XLR combo socket which was shipped with the sub really didn't in my opinion provide a good connection so I bought a proper RCA to XLR adapter which fits nice and tight. I really hoped this would cure the drop out but it didn't.
When I say I play a 35 Hz tone at normal levels I mean, I want to feel the sound. I am not over driving the speaker. I check the cone throw and it looks quite OK. With an EP500 I expect to feel the sound and when it works properly, it sounds very nice (when not buzzing/vibrating).
I am pretty sure the buzzing/vibrating originates from the sub because if I press on the back amplifier panel near the high level in (top right), the buzzing almost completely stops. It must be something loose but I did remove the amplifier and everything looked tight. It will almost always vibrate when I play a low frequency tone which you know I don't really mind as long as I don't hear it when watching a movie but I have heard it watching movies.
A few mentioned to turn off Audyssey but I completely disagree, I have had it with two Denons over the last couple of years and it works real well especially with the 4311. Dynamic EQ ON with Dynamic Volume on Day works awesome at low and high listening levels.
