Also, if like me you have a 2010 model, the software is only coded up to an iPhone 5. Not my iPhone 5s. There is no software update option until the late 2010 models when they added the combox. My iPhone doesn't even work with the Y cable.
However, I have a 64Gb, USB 3.0 memory stick reformatted to accept FAT32 which is all the system wants to play with, with over 2000 tracks on it which plays perfectly well. No distortion, sound reduction, interference etc, and sounds just as good quality as the cars hard drive.
I just cut and pasted the music files from iTunes onto it.
The only mildly irritating part, is that because it files the tracks alphabetically, when listening to an album where it matters, you don't get the tracks in the intended order. You get them alphabetically.
Otherwise it works extremely well.