This guy from the forum (outside of it) exchanged this with me:
ME: Is your ITL and XML, Artwork and other folders iTunes creates when it is installed, still in the C: drive Music/My Music folder on your desktop?
HIM: NO I told Itunes to create those files on my I partition. I explained this, bill, I told you I did that so that the path would be ALMOST the same as what I thought Plex would need with only a minor change in the path.
HIM: When I created my brand new iTunes library from my PC what I did was I told it to create the iTunes library on that I partition, it could have been anywhere but I put it on the Synology purposely so I could see the path.
HIM: I manually copied the same structure of my music library DIRECTLY to the Synology. So, Itunes only had to create a NEW (identical) library to reindex it (in that mapped folder on my synology - also known to you as my I drive).
Huh? I'm lost. He said he created a partition, " I ", and MOVED his iTunes library to a folder called iTUNESXML. How can he keep the metadata/playlists intact, and how does iTunes program even open if you move it from you C: drive - unless I misunderstand him. Remember, this is all so that PLEX can see the XML files and then playlists feature to import into Plex will work.
Another comment I'm confused by:
HIM: You are confusing mapping of drives. You don’t see :”MUSIC” in the location for Y, because Y maps it FROM the music drive, in other words, we are already sitting INSIDE the music folder, i,e, you might say the MUSIC FOLDER = Y:
The mapping of my PC is IRRELEVANT!!! you need only concern yourself with the SYNOLOGY. So, stop asking questions about mapping. THE ONLY THING important about mapping is related to the file path that itunes creates and you must edit so that Plex knows its local/on the synology.
Here's a layout of how he explained himself. There's a lot of missing pieces in my opinion. I appreciate he's trying to help, but I just don't get it. 



If you have any thoughts, that's great, but I understand if you don't. Deeply appreciate it.