Setting up subs is always a challenge because the room and placement have such a big impact. Let's start with the easy ones...
My very first thoughts would be that (a) some of the bass management (crossover) settings in your receiver are not right, and (b) the level on the sub is turned up too high to partially compensate for the funny crossover settings.
Can you walk us through the basics ?
1. What kind of receiver ? What are you using for input (DVD, CD etc..). How is the DVD player connected to the receiver ?
2. How is your bass management set up ? Are the M80s set to Small or Large ? How about the other speakers ?
3. What is your crossover frequency set to in the receiver ?
4. What are the settings on the EP500 ? I forget if it has a "crossover disable" switch but if it does is it set to "enable" or "disable" ? What is the crossover on the EP500 set to ?
Probably more questions will come but that is a good start. We'll get this figured out
BTW please don't be offended by the "start at the beginning" questions. I went from an EP350-class sub (PSB 6i) to a bigger / better sub (SVS PC+, decision made before the EP500 came out) and found the deeper bass of the new sub brought brought old problems to the surface much more dramatically. The new sub also fixed some problems (boomy pop music despite much time spent on placement) which was nice and an unexpected bonus.
It is definitely possible your EP500 has a problem but it doesn't seem that way yet.
