(1) That could be a good idea. Afterwards, report the status of these three...
"
Onboard HD Audio
Enable/disable onboard HD audio. Set to Auto to enable onboard HD audio and automatically disable it when a sound card is installed.
Front Panel
Enable/disable front panel HD audio.
Onboard HDMI HD Audio
Enable audio for the onboard digital outputs.
"
Edit: Well, a reset to defaults in BIOS won't be a problem unless you've switched from UEFI to Legacy mode before installing Windows. You said you haven't done that. Going to Defaults just affects settings you have done.
But I'm unsure what pulling the CMOS battery will do -- will it restore the factory state BIOS of the computer? Then be prepared to flash it afterward with the latest version from your site.
(2) I might, though, just before that...
(a) Replace the Asus VP278 monitor with the one that has no speakers.
(b) Uninstall...
both High Definition Audio Controller's under System Devices,
Asus VP278 under Audio Inputs & Outputs, &
both of them under Sound, Video & Game Controllers.
(c) Reboot.
Good luck.