What is a DJ? Everyone who considers him or herself one can probably give you a unique answer. Is everyone with a music collection and a sense for good timing a DJ, or does their music collection have to exceed a certain number of gigabytes or slabs of vinyl to be in the club (no pun intended)? Audio playback devices are certainly getting more plentiful and powerful on a large scale; anyone who's played with an iOS DJ app can tell you that. In the deeper end of the DJ pool, things aren't expanding at such a frantic pace. But every once in a while a new toy crops up that adds depth and breadth to the way music nerds play back music. Na