I've been searching and reading on the forums and Google but either I'm too stupid to understand what's been written or my question hasn't been definitively answered (and I'm willing to concede that the former is the more likely scenario).
I've got a Synology DS412+ running DSM 5.1-5004. I've installed the iTunes Server package (1.3-2361) and the Plex Media Server (v0.9.11.4.739-a4e710f).
I created a share called Music and under it created a folder called iTunes. I then copied my entire iTunes folder structure from my PC to the NAS, including all the "iTunes Library*.*" files.
I then went into the Plex Media Server configuration > Channels and checked the "Enable iTunes Channel" checkbox. In the Advanced Settings I entered "/volume1/Music/iTunes/iTunes Library.xml" into the "iTunes Library XML Path" field.
Finally, I went to DSM and stopped and restarted the Plex Media Server.
But I still don't see iTunes under Channels.
