Several problems and confusions in your post.
iTunes does not use the .xml version unless you import it. Note that references in the .xml do not have date added, playcount, or ratings. Typically you import the .xml to a blank library as part of rebuilding a broken library. Importing essentially re-adds the links to the new library and the date added will be the current date, not the original one.
Changing media location in preferences only has iTunes deposit new additions there in the future. It does not get iTunes to read the location for things you may have moved yourself in Finder.
A "library" is a complete set of library files plus media files. You say you want to move your library but only mention media. What do you want to do? (I strongly recommend you move all the library intact to the NAS. Just about every post I see with mention of NAS is some problem iTunes has in keeeping track of files which is made worse when people split their libraries. I suspect getting iTunes to work properly with NAS is luck not design.)
Quick answer on moving entire library if you use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive. Open iTunes and immediately hold down the option (alt) key (shift on Windows) so you get a prompt to select a library, then guide it to the 'iTunes Library.itl' file in the moved iTunes folder.
If you put the copied iTunes folder in the default location of Macintosh HD > Users > *User Name* > Music then you don't even need to start with the option key held down, iTunes will automatically look for it there. (Make sure there isn't anything already in the iTunes folder there that you want to keep since you will be replacing it with the one you are moving.)
Longer answers if for any reason you do not think all library files are inside your iTunes folder (changed preferences settings at some point):
iTunes: How to move [or copy] your music [library] to a new computer [or another drive] - http://support.apple.com/kb/HT4527 - a somewhat bewildering and not always easily understandable set of options.
For the record there's this reference for iTunes 11 but it really doesn't strike me as having the specifics you need. iTunes 11 for Mac: Move your library to another computer - http://support.apple.com/kb/PH12168
2011 ilounge article: Transferring your iTunes library - http://www.ilounge.com/index.php/articles/comments/moving-your-itunes-library-to -a-new-hard-drive/ - An article with good background information (similar to the links above), particularly if you are not sure your media files are all grouped for quick answer above. Unfortunately under the single term "transferring library" it describes two very different moves; relocating just your media (not really transferring your library and not recommended unless you really need this configuration), and relocating media+database (really your whole "library"). Make sure you understand the difference before electing to move only media.
What are the iTunes library files? - http://support.apple.com/kb/HT1660
More on iTunes library files and what they do - http://en.wikipedia.org/wiki/ITunes#Media_management
What are all those iTunes files? - http://www.macworld.com/article/139974/2009/04/itunes_files.html
Where are my iTunes files located? - http://support.apple.com/kb/ht1391