That's strange; Samsung wrote their kernel to play nice with their factory grown ROM to pass all 'musical' audio through to a DAC when plugged in. If it only plays in USB Audio Recorder Pro then that means there is a driver conflict as USB Audio Recorder Pro has its own drivers that override all of Android's.
Personal side-note: I think that the guy who did USB Audio Recorder Pro should write a program that was specifically a music player that used the same drivers. That way even devices that have poor or no USB audio implementation should be able to use their DAC's.
Edited by gidgiddonihah - 2/28/13 at 11:15pm