If the room is open on two sides then there is a pretty good chance the sub is just too small for the room. Only other possibility I can think of, depending on the receiver, is to push the crossover frequency way down and rely on the M60s to carry some more of the bass. The M60s go pretty deep on their own, maybe if you only ask the EP125 to carry the lowest notes you can get the "oomph" you want without overloading the sub.
The EP125/M60 combination sounds like an unusual one -- M60 is -3db at 37 hz while EP125 is -3db at 35 hz. Did you have smaller mains before then upgrade ?
I would try the following :
- set mains to "Large" if not set that way already
- set crossover frequency on EP125 to 40 or 45 hz, maybe start with 40 and go up from there
You may already be set up this way, of course.
The other obvious thing is to make sure your sub is positioned as well as possible to maximize bass output, usually in or near a corner unless you are right near the middle of the room.
Have you done the "put the subwoofer in your favorite listening chair then crawl around the room pretending to be a subwoofer and looking for the spot where you get the best bass" trick ? If not, that might be a good idea. You will probably need a longer subwoofer cable than you have now, everyone else does
