Android music server over usb

Hi i have two stereos in my car, one being a high quality single din media player, the other, a 7" android car stereo. The Android device is a super cheap Chinese device that sounds awful music quality wise but having the freedom of easily using the touch screen for music is a plus.

What id like to do is use the Android system to serve music to the single din stereo over usb, this possible? Obviously it would have to appear as a mass storage device and I would want the freedom of switching the mounted I guess 'virtual usb disk' on the fly Is this possible?

 

It does have bluetooth but the issue is the source of the media file would be coming through the terrible cheap headunit.