The EP500 is a very capable subwoofer but not knowing the THX Ultra standards I couldn’t say if it meets them. Could you post a link to the THX Ultra standards? AFAIK THX is pretty tight lipped about their requirements.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1