RNS-E 2006 A4 Cab , how to add USB support

[djt100]

Hi Have a 2006 A4 Cabrio, with the RNS-E nav system and the Multifunction steering wheel. It has a CD changer in the glovebox, but I'd prefer if possible to add a decent bit of music in the car with say a USB full of MP3's is this possible or if not then bluetooth stream from the phone ??

Any recommendations, Don't want to spend fortunes, just like some enstra sounds in the car