I did a lot if googling on this topic and reached the conclusion that for all the hassle and uncertainty it was just as simple to buy Tunespan for this task. I have transferred my entire collection of movies and TV shows onto my NAS and left my music on my MBP.
Everything works well, and I can move files around from NAS to MBP whenever I want, so long as the NAS and the MBP are on the same network.