Steven - I agree that your initial thought are probably right. Sounds like your room is a huge volume to fill and if you are use to something that just moves lots of air w/o regard to detail then the EP500 might not feel right.
A couple other things you could try:
Place the sub right in front of your listening position aimed at you. Having it near field may increase the slam w/o the muddiness.
From you’re initial post I’m supposing a second sub is out of the question? Assuming so have you ever tried a Buttkicker or other tactile transducer. It wont quite slam your chest but it will rock your seating giving you very low bass w/o the high SPLs that make everything in the room shake. I used one in my apartment to make up for not being able to turn up my subwoofer (yet to finish my seating so I can set it up in my house but I will use it). It lets me keep the SPL from the sub down enough to keep the bass tight and punchy while still feeling the earthshaking rumble in my bones when appropriate.
