Ha! I was curious about this too and bookmarked a review. Anyhow, here is the pertinent info in regards to the dragonfly:
"So this hasn't gotten much publicity, but under iOS 7 you can now use USB DACs with an iPhone or iPod Touch (in addition to the iPad, which has worked for some time) via Apple's Camera Connection Kit (dock version) or Lightning to USB Camera Adapter.
If the DAC draws more than 100 mA (the DragonFly does), it must have its own power source, such as a powered USB hub. I've tested the DragonFly with a powered USB hub and iPhone and iPad and it works great. "