I've actually tried it a few times, first time I didn't clear the device but it just started copying all my music across and it ran out of space pretty quickly (there was only about 5gb free). So I restored it in iTunes which removed everything and then tried to sync again with Musicbee, which is when it crashed with an out of memory error. Restored it again and tried to sync again but I got the same problem, so let iTunes put all the music back. I'm using the default sync settings in Musicbee, no conversion or volume levelling.