I'm pretty sure that my itunes rips to .m4a which the car will play.
I did discover over the weekend that it does not appear to support .wma lossless - supports .wma but not lossless - bit of a bugger as all of my music is in lossless format. I've elected to go with 320 kbps .mp3 which is all but lossless quality. It's a quick and painless job to convert using something like dbpoweramp batch converter.
Another point I picked up on was that the car does not support the NTFS file system for those of you planning to use a portable hard disc. The hard disc needs to be formatted FAT32 - which most are by default.
Tried an ipod Touch (latest firmware), SD card and portable HDD and the HDD seems to have a very much quicker response time than the former two.