I have a Kenwood MusicKeg for sale. It's essentially a Phatnoise Musicbox, but made by Kenwood. It comes with the in car cradle, a USB cradle, 10 GB cartridge, a BMW/MINI specific adapter (provided you have the 6 and 3 pin connectors, and all MINI's I know of do) that does work in the MINI, and a Kenwood FM modulator in case you want to use it in a different vehicle. Works like a charm, I've had it in two vehicles without any problems.

A couple of things up front, you can only have 600 songs in a MINI. It works on the CD changer input, so you can have this and another input. Ok, so that was one thing. $200 + shipping.