I've created a new utility called RoadMusic to help transfer iTunes playlists to an SD Card which work in the RNS-E head unit. I know there are others out there, but they didn't do exactly what I wanted, so I created my own.
It takes into account the many limitations of the RNS-E, such as the file/folder size limits, unfriendly file names, playlist size limits etc. If you have a number of SD Cards, then it will help you split your library across them.
So hopefully it'll take some of the guesswork out of loading up your tunes. I've also made it fairly user-friendly.
The app will currently only work on a Windows PC with iTunes installed. I have version 10.5 and I've only tested it with this version. You will also need to have the .NET Framework 3.5 installed.
IMPORTANT: The RNS-E only plays MP3 files. So this app will ONLY deal with MP3 files and the app will not convert any other type of file to MP3.
This is V1.0 so I don't expect it to be flawless, but it works for me, so if you have any feedback then let me know on this thread. To diagnose any issues I might ask you to send me your "iTunes Music Library.xml" files and any problem MP3s.