I also used to use my ProPioneers with Win7 and have moved to a MBA. Yes, OSX is different but it's easier to use and more stable (IMO), but then I did use Ubuntu Linux for a while (OSX is very similar in lots of things).
But, to your question. I haven't shared anything in Preferences. Instead I mount the NAS share in Finder using AFP.
I also have iTunes on the NAS, but split into Music (a share called Music) and Library (a share called iTunesLibrary).
I presume that the iTunes that is running on the MBP can access all your Music OK and you can manage the files and add/delete stuff OK.
What do you actually want to do ?
1. Backup your iTunes Music and Library to the NAS
OR 2. Make the NAS your repository for your Music files
OR 3. Make the NAS your repository for Music and the iTunes Library
It might be a simple matter of user permissions on the NAS share that you are attempting to connect to.
If you look in FInder>Go>Connect to Server you should see your NAS listed as something like : afp://NasName%20(AFP
If not then your MBP can't see the server.
Let me know some more details and we'll see what might be possible.