I am a Sprint employee and Epic 4G owner (for a little over a week) and have no problems streaming stereo to my Moto S9 stereo BT headset. I can stream direct from Pandora, the built in Music player as well TuneWiki, no problems with any of them. There's nothing I did special. I paired my Moto S9 headset like normal and it auto detects it as A2DP streaming compliant.
Having owned almost a dozen BT headsets over the years, and even a few mono-ear models that "support A2DP" streaming music, I've had the worst luck with getting reliable music streaming to non stereo BT headsets. I know you said your Pre did it, but guessing the Epic doesn't use the same BT chipset and certainly not the same drivers (different OS).
Hopefully a near future update will resolve this minor issue. Thanks for being a Sprint customer and new Epic 4G owner!