What's the best way to control audio throughout an entire course? I would like the option to toggle audio on/off.

Hi Robert,
Probably the easiest thing to do is to mute the audio with an action like the attached image, where clicking the mute button sets the audio to 0, and shows an UNmute button. Click the unmute button does the opposite. You can stack the buttons on top of each other. I'd set this up on a Master. The "set lesson volume" action block can be found under the Page category.

Hope that helps!