Audio To Expression for NPCs?

I'm considering using Audio To Expression for NPCs. However, I can't find documentation on fundamental aspects, such as how to pass an Audio Source to OVR Face Expression.

First of all, is OVR Face Expression something that can be used independently from an HMD?
If that's possible, could you provide an overview of how to set up OVR Face Expression for NPCs instead of the player's avatar, as well as relevant documentation?