ive mentioned it in the bugs thread and asked a dev to see if he can remedy it.
until it gets fixed by a dev or google/htc/sprint i found a free app that will fix it for us.
and it does work.
google play search "soundabout"
make sure you check off wired headset detection, and select "wired headphones" in the [media audio...] selection box.
voila, you got sound to your aux adapter or for your car now.
the only issue i see is the builtin music player doesnt let you choose EQ and the beats options is still greyed out.
so you might want to experiment with other 3rd party music players with an eq if you want better audio.