Unless I’m misunderstanding your ask, you should be able to install the Audnexus agent, which will make it available in the agent dropdown in your library’s settings (a PMS restart may be required).
Keep in mind though that Plex is planning on completely ripping out the legacy agent system in the near-ish future, which will include third-party agents (and it’s already been done on Shield servers). When that does happen, the maintainers of Audnexus would have to release a new version that works with the new API Plex is working on (Fireside Follow-up: Metadata Agenda, NFO Support, and some of our future work on PMS - General Discussions - Plex Forum).
