EXCEPTION thrown ('fmt?') popped up while trying to work with AVFoundation on the Apple TV simulator. A little searching and, I googled across this Stack Overflow post that suggested changing the input in System Settings might work.
I don’t have “Internal Microphone” in my Sys Prefs Sound > Input pane but I do have “Line In”. I chose that. My output was already set to Headphones. That one change got rid of the issue and my ATV app is now running with sound.
Thought I’d leave this here for future googlers.