Although protected songs purchased from the Apple Store can be played with a bluetooth connection to your iPhone, if you copy those songs to a USB flash drive, they cannot be play in the Model S.
Here's the simple solution:
Burn your playlist to an audio CD. Then import that audio CD back into iTunes as a new play list or just let it overwrite your existing songs. The newly imported songs are no longer protected. They can now be copied to a USB flash drive and play through the car's music system.