There's already a thread on this, but other than a detachable cable and new earpad it's the same headphone sonically.
It's cheaper to do the mod yourself or buy a modded M50 from soundprofessional.
Tbh I'm a little more interested in the M40x.
Edited by RoMee - 1/26/14 at 9:30am
NAMM 2014 PRESS RELEASE: The original ATH-M50 has been praised by leading audio engineers and journalists worldwide, and now the ATH-M50x features the exact same coveted sonic signature as the original, with the addition of refined earpads and three detachable cables (a 1.2m-3m coiled cable, 3m straight cable and 1.2m straight cable).