I've tried:
  • choosing different in-game eq options
  • toggling mute on the various volume sliders in-game
  • toggling mute in windows sound mixer
  • plugging in a usb HyperX Cloud II headset (has its own sound device)
  • switching from add-in card (soundblaster) to motherboard sound (realtek) and changing default device
  • changing to monitor speakers (nvidia audio), setting that as default
  • disabling nvidia's virtual audio device (from another post somewhere)
  • disabling and re-enabling the sound devices in device manager
  • routing the sound through nvidia broadcast (out of ideas at this point)
Sounds continued to play from other programs (Discord, web browser) with the various changes. It was solely FFXIV that lost sound. As I couldn't think of anything else, I closed the game and restarted. Sound started working again for it in the title screen and continued to work after sitting through the queue again.

I really am starting to think this is all related to the Immerse audio stuff, as all of my sound issues only started after 6.0. The last time I had a sound issue, I lost everything besides the BGM. Wondering if it was some issue with realtek (motherboard sound), I installed a soundblaster ae-5x which was what I was using when I lost sound completely. It doesn't seem to matter what hardware is being used.

Also thinking about the Immerse stuff, since it's a sub, how and when does it check if your account is active for it? Is it doing it while you are playing? I haven't a clue as I have no interest in it (I don't normally use a headset so its of no benefit). I did find in one of the faq's that unlike the other immerse software, the ffxiv one is rendered inside the game itself so who knows what the game is doing to check if the Immerse option is checked off and if you have a paid sub, etc.