The way I do it is simply create a folder for each itunes playlist. Drag and drop all the songs in playlist A (itunes) to folder A, Playlist B to folder B etc. On AK100 when u want playlist A, go to folder slection and pick folder A
When you add more songs to your itunes playlist, drag and drop in to it's corresponding folder on AK100 and it will say XXXX songs already exist, do u want to copy them anyway? select No and only the new songs will copy
after you set it up initially, consequential syncs are literally a drag and drop away, extremely easy