Someone was able to get better text-to-speach on Mac? Why I can't select Siri voices?
Looks like addon is also ignoring downloaded enhanced versions from VoiceOver settings.

It's a WoW issue. On Windows players can download NaturalVoiceSAPIAdapter, third-party software, so WoW can discover advanced TTS voices installed on their PCs. But I don't know if there is an equivalent for Mac.