As many people know, there are a few shows that aired in an order differently than it was released on DVD. TheTVDB (Plex's default TV metadata source) tracks both, but shows air date by default. This creates a problem with Plex because it will always grab the info using the aired order.
When I found out about this, I tried to look for a solution and I found a metadata agent that someone on these forums created, but the development seemed to be dead, many people were reporting problems with theme music, and the thread was frankly a mess.
Thus, I tried to find the newest version of the agent I could and I have put it into a GitHub repo for easier access. I also forked Plex's theme music agent to add support for the DVD Order Agent. That fork is located here.
These plugins should work alongside a normal Plex install just by putting theme into the appropriate Plug Ins folder. If there are any issues though, pull requests are 100% welcome. But, disclaimer: I don't know much Python, so don't expect me to be releasing bug fixes or updates to the code, I just wanted to make it easier to find and fix the theme music issue.