What do you mean: the jury is still out? I am right here. I used to drive an Audio Technica ATH-A5 with my Earmax Pro for quite some time, and the amp worked fine at the 60 Ohms nominal impedance. To my ears, bass extension, impact, control and timbre was better than anything one could get from the Senns HD 580 or 600. I have compared the Earmax Pro to the solid state "Naim Headline" as well, and - as was to be expected, especially from a Naim product - it had even more punch, but it was more brute force than superior musicality in the bass region. There was certainly more elasticity and timbre with the Earmax Pro.
Nowadays, I use a Beyerdynamic DT 990 Pro (250 Ohms) with it, and bass performance is the best I have ever heard from any headphone - to my ears, both the Senn 580 and 600 aren't all that great to begin with, in terms of smoothness, dynamic range, tonal balance, and bass extension and impact.
My version of the Earmax Pro is called "Brocksieper Pro", though. Because this is the name of its German designer: Stefan Brocksieper. And my power supply unit works with 220 Volts. I think this might account for differences in performance. But this is pure speculation.