I've never heard the EP350, but I bought the EP500, and I have no regrets. Like you, my listening area is small enough where a 350 can handle the volume without issue. But I wanted to go deep. And from my experience to this point, the EP500 goes deep AND loud. Axiom's claims of down to 13HZ in a real room sound realistic to me based on my experience. Even in an anechoic chamber, the EP500 goes lower than the audible frequencies.
Compared to my old Mirage dual-8 inch sub, there's no comparison for the low frequencies. The 500 produces unstressed tight bass at all frequencies.
Beware though... you will probably have to be satisfied with never turning the volume knob past 3 on the 500. Its just got tons of power.
