The cafeteria PA box is part of the old AV crew infrastructure. It is sometimes used to toggle the cafeteria speakers for Radio L'Am and quick events.

I filmed a video about it a while ago, which is available here: https://youtu.be/LbowNXDhWUk

In short, this was built back when the Market Square had hanging speakers, and the drama room used in-ceiling PA speakers, both of which haven't been around for very long.