I have moved my iTunes library and files from my iMac to my Synology RS814. Now I can:
Rip a CD to my my iTunes library on my NAS.
Play music from my iTunes library on my NAS to my iMac
Play music from my iTunes library on my NAS to my Sonos devices
It works so well, and was so simple to do, that I have to wonder if I am missing something after reading all the confusing posts about this. Please comment and let me know if that is so.
First, I configured my iMac so that the iTunes folder automatically mounts whenever I start or log in to my iMac. That way the iTunes folder on the NAS will always be always be available. Here is how I did that:
1. I manually mounted the folder I created for iTunes using Finder > Go > Connect to Server
2. System Preferences > Users and Groups > Login Items
3. Click + and select your NAS server in the sidebar, then double click the folder in which you have your media files and press add. If the folder is several folders deep, just keep clicking through until you get the one you want to be automatically mounted.
Next, I just copied everything from the iTunes library on my local hard drive to the music directory on my NAS. Once it finished, I renamed the iTunes folder iTunes_old just to avoid the possiblity that iTunes would try to find it.
Then, I held the option key while starting iTunes and chose the iTunes folder on my NAS.
I selected some music and checked "get info" (right click on a song to get the "Get Info" option) to be sure it was on my NAS. It was.
I wanted to be sure nothing would go wrong with my iPhone backups since they use iTunes for the back up procedure, and did some research, and found that the iPhone backup is not in the iTunes folder...it is kept in ~/Library/Application Support/MobileSync/Backup (hold option key and select GO in Finder to see the library folder). I performed a manual backup, and the date and time of the file in this folder updated showing it was still going to this location.
But strangely the apps themselves are backed up in the iTunes library, I wanted to be sure they would continue to be backed up, and found that they were not.
After running a manual backup, there were no files on my NAS at /Volumes/Music/iTunes/Mobile Applications.
Even though the app icons were displayed in iTunes (click on Apps on the iTunes sidebar), when I tried a "get info" on the app, it could not find it. For some reason, the backup procedure thought all the apps were already backed up (and they had been). To force it to make a new backup to my NAS, I deleted all the app icons in iTunes, then manually backed up my iPhone, and all the apps are now on my NAS at /Volumes/Music/iTunes/Mobile Applications.
Of course, I still have the backups that were in my original iTunes folder at ~/Music/iTunes/old/Mobile Applications.
One note about the Sonos--any time I add a new CD to iTunes, it is necessary in the Sonos Mac app to click Manage>Update Music Library. This loads the contents of the current library into the Sonos device's memory. It does this in the background and not disturb any songs that are currently playing.
My NAS is set up with a Raid 1, and also does hourly backups to a 4 TB USB drive using the Synology Time Backup app. Raid is not a substitute for backups. I would not move iTunes to a NAS from a Mac that was getting regluar backips using Time Machine unless the NAS itself has a way for it to be backed up.
FYI, running 10.9.2.....