USB
As far as I know, at the moment there are no phones with USB audio drivers available.
Would be great to couple your Android device to a USB DAC and play its content using asynchronous USB.
Probably the best method to get top quality bit perfect audio out of the phone.
Archos added support for USB DACs in December 2011
I found one company producing USB Audio 1.0 for Android.
There is a lobby going on at the Adroid Bug Tracker to include USB Audio support in Android. Join!
© Vincent Kars February 2012