Thank you so much for taking time to investigate the issue. What you've reported is incredibly baffling though. So, if I've got this correct, all game audio works except the user voice playback, which will only play if you've chosen your speakers as the output device?
And the waveform appears for the voice clips, but not the user voice recording, but the user voice is actually recorded? That's the weirdest part, because the waveform sampling and user recording uses the exact same audio bus. ...what on Earth...