You could think of the sync as one-way, so that on your laptop you get the files and do all the metadata (grid) et rest arrangement on this side, this by exporting the iTunes playlist/files into your own Traktor playlist. But yes, you can’t sync back the changes to iTunes, you need to copy the whole playlist via an USB stick or something similar to other devices in case you need the info on those. Basically I collect the material I play on my main laptop and save it off to an USB stick (the playlists NML file and files) and this way keep the data intact.