I really don't know. I assume you mean the 6FL retrofit and all the info I have seen on that is for non iDrive retrofits. Forum user Technic is the only one I can think of that might know more about this. At any rate, I don't think it requires any firmware updates (if you can play MP3s already), just coding changes to the VO and CAPPL.
I added a Dension 500 to my system and I only use a thumb drive with MP3s. It supposedly works with iPods but I've never hooked one up to it.