Of those that I have, or have had, in my inventory, the AR9s win in the bottom. EPI A500s are almost indistinguishable from the AR9s in this area, which is pretty surprising considering the means of production. The AR9s have 2 active 12" woofers, and a nice large resonating chamber. The EPI A500s have a single, deep-throw 10" woofer and two passive 12" drivers, with a decently sized resonating chamber. Both models have their 12" elements in the same locations, side-firing, positioned at the bottom ends of the cabs. Overall, the AR9s produce east coast sound (articulate and sweet), while the A500s produce a more west coast sound (in your face and bold), but their bottom ends are indistinguishable. Both require serious power to wake them up.
Enjoy,
Rich P