Default Taunt sound requires https://wow.curseforge.com/projects/sharedmedia_causese
Make sure your master volume slider in wow's sound options is maxed out and reduce slider on other sounds.
"Sound at x stacks" plays the sound when your Co-Tank reaches the specified amount of stacks. (0 = disabled)
This is not pre-configured for the most part.
Let me know if something is missing/wrong.