How large are your playlists? And how large is your collection?
I remember a buggy Firefly svn version (not the one you’ve installed, some time back, just for clarification of some time issue) which took eternally to load… which was back then due to the fact that it listed all songs under each playlist. Now with say 10.000 songs and a dozen playlists, it suddenly had to transmit 120.000 entries…
That’s just to say that large playlists may take up additional time on connecting through iTunes (not sure why they do not download them just on request – the protocol would allow so).
Since from the same NAS here, it works quite faster with a Roku Soundbridge, I assume it’s the way iTunes operates and the size of the database combined, not the fact that the NAS may be slow.