The use of the same driver in the EP350 and EP500 was also confirmed in the audioholics review of the EP500:

http://www.audioholics.com/productreviews/loudspeakers/AxiomEP500reviewp3.php

"Thanks to the benefits of lower cost with high volume, Axiom was able to incorporate this same driver design in all of the 12” subwoofer systems including the EP350. "