I will throw this out there, I have not heard the EP500 but have heard the EP600 and the STF3 at the same time and I feel the Axiom subs(the 3 I have heard) are more musical with their expansive smooth sound, while the Hsu STF3 was great for HT impact.

Is there no one nearby that has an Axiom sub for an audition?

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70