Here's what Numark have to say...
We've updated our powerful, highly isolating, folding headphones for 2010. PHX becomes PHX USB with a new detachable cable that enables you to plug directly into USB and cue from software without an additional audio interface! PHX USB also comes with an analog cable for use with mixers, CD players, and other traditional gear. Two sets of earpads, a plug adapter, and a carry bag round out these killer cans.
Pricing and Availability: