Easiest way is to get an OEM CD Changer made after September 2005, they play MP3's and WMA's. Next easiest is to get something like an Alpine CHA-S634 (Physically almost identical to the OEM Changer), KCA-130B (AI-Net to MBus adapter) and an iBus -> MBus adapter from the likes of Soundgate, Connects2 etc.