I've been wondering this for ages.
Would it be possible for Android to drive a USB DAC? Like if I was to somehow get a micro usb to mini usb cable, would we be able to actually use the snd-usb-audio linux kernel module with the Android OS to send audio output? It seems finding such a cable might be a trick. (One might have to settle with a micro -> usb a female, usb a male -> mini deal.) ...
But just what do the hurdles look like on the Android side? I'm sort of surprised I've never heard any discussion about this.
Imagine strapping a DAC/amp like The Predator to a Droid for a truly bad ass headphone experience on the go.