There has been lots of questions about adding USB/memory card adapters to cars that don't have the facility. I used carry about 100 CD's in my old car which had a 10 disc CD player in the boot as well as the player in factory Sony headunit. Then I added a Connects2 iCoonect USB adapter that used the Sony CD changer socket. It has a through port, so I could still use the CD changer.  Now I have my Mk3 and the first thing I added was a Bluetooth/micro SD/USB/AUX adapter. It can use a 32gb mem