What JackD said. And there are loading options are 100 ohm, 200 ohm, 1k, 10k, and 47k.
The Insight is the same signal path circuit but that's wall powered for an extra $400. You get 1,200 hours out of a set of batteries, plus the benefits of quieter soundstage, so the PH3D is the way to go in my book.
