You have more music on your ipod than on itunes - you want to sync them but keep the music you have on the ipod as it includes what you already have in itunes plus more - how to do it without wiping s?

Try unticking all the songs on Itunes. And add tick ONLY the songs you want to sync into your ipod. Itunes will only Sync the ticked songs. The rest of the songs on your ipod wont be erased.