Instead of messing around with the internal HDD, which is a major PITA IMO, just load your music onto a USB flash drive and plug it into your USB port in the center console. Its so much easier especially when adding or deleting just a few songs. I have a 32GB OCZ Rally2 and been using it for over 2 years now. No problems at all.
09 E90 M3 - Interlagos Blue / Black Novillo / Sycamore Anthracite / Eibach / HRE