Windows Phone 8, Music through car stereo

I always use Bluetooth streaming to listen music in my car and never tried using the USB port. Recently, I bought Xbox music pass and downloaded few songs to my phone. I tried playing them through my car USB and due to DRM restrictions they did not play. I wish they change this policy, if possible. I understand that Record owners won't agree with this.

Sound quality through USB is significantly better than Bluetooth streaming (I am not an audiophile and never payed attention to this). My concern with this is that I can't listen to navigation direction coming through my phone. Unlike WP 8, in iPhone you can listen to directions as well as music through car USB at the same time. It will be awesome if MS can bring these changes in WP 8.1. I don't mind using a proprietary cable instead of micro USB. I think micro USB is the culprit here. Hope wise people here in The Verge can explain why this cannot be done. I see that android has the same problem where it cannot play music as well as give directions through car USB.