The standard changer will play copied audio CD's but doesn't support mp3. For mp3 support you need a Sony package, which comes with the adapter so it's plug & play. The HU doesn't care, it's just audio by the time it gets it but you will be restricted to 99 tracks per CD in mp3 format. addachanger used to do a Sony mp3 package for Audi for around £170 but they don't seem to do it now. You may have to buy the Sony changer and add the interface separately.