With a sub, you really don't need to worry so much about a "match". It produces LFE and that's all it does so the timbre matching isn't an important consideration.
An EP500 is an awful lot of sub for the room you are in. I agree with spiff - an HSU VTF3 or and SVS PB-12 ISD (or 20-39 PCi) gives you a great sub at a reasonable price that will grow with you .
I use the 20-39 PCi in a 16x22x10 room and still have plenty of sub left.
The EP500 will absolutely do the job for you, but the other alternatives will have the added advantage of saving you some money as well.
You can't really make a mistake with any of the subs I've mentioned. Unless, of course, you invite Ajax or MarkSJohnson over to listen with you!!
Pick the sub you like and abuse the credit card with confidence.
