One of the two necessary components for a discussion about an Artist and an Audience is the existence of an "Artist." Literary criticism contains an infinity of iterations on this theme, but for the purpose of Vexila regis produnt, a psalm from the 6th century it's fair to say that the Author is "Unknown."
Vexila regis produnt is the earliest specific song that is mentioned in Henry Raynor's comprehensive A Social History of Music from the Middle Ages to Beethoven.
So, to the extent that you sit at your computer and actually listen to a gregorian chant once in your life, this is the one to listen to- Vexila regis produnt.
It goes without saying that much if not all of "music history" from the Middle Ages is "church music." The first generation of Artists to burst out of the Church music scene moved to playing for Royalty, I imagine communities of musicians in the late middle ages gossiping about which was the better gig, and where you might go next- but there aren't really specific guys who have survived- just songs.