Just for fun, I was listening to the various sounds effects and music tracks from MOUL using Windows MP and just calling up the isolated files from within the Myst ONline file. (If you want to do this, you can find the files in the Program Files on your harddrive, then Myst Online, then sfx, then streamingCache.) You can't always tell from the file name which is which, but you can hear the various sounds in isolation.
However, I couldn't find everything there. For example, the music you hear around the library in Ae'Gura doesn't seem to be there. So, either I just can't find it or recognize it or the music files are generated not only from within my PC but perhaps on the main server as well? Does anyone know?