Windows – No audio in newer games on Windows 10

I'm on the latest Windows 10 1803 17134.48, running on a ASUS ROG Maximus X Hero Intel Z370 motherboard with Realtek audio. Speakers are plugged into the headphone (green) jack in the back.

The hardware (and the Windows install) is 7 months old, and sound has worked great everywhere for most of that time.

Recently I do not get audio in most games. Audio still works fine in non-games (e.g. VLC, Chrome/Youtube etc) and in some games (older games?).

This makes me suspect that the problem is with Direct X / DirectSound, but since there is no way to install / reset that in Windows 10, it's hard to tell.

"Speakers (Realtek High Definition Audio)" is always set as the current audio device. When in e.g. VLC I can see the audio meter move in the volume mixer, but in games there's no output there.

Sound in games where Realtek is not working works fine when played thru a different sound device (a USB headphone amp with its own DAC).

I've searched for clues, here's a non-exhaustive list of things I've already tried:

• Deinstalled all other audio output devices that I am not using, such that there is no chance it can be switching to another. There was Nvidia audio or output to my monitor that is now gone, and there's only 1 audio device left (speakers).
• Checked DxDiag.exe to see if there were any errors. none.
• Checked Device Manager for any problems.
• Tried reinstalling Realtek drivers. Neither the February 2018 ones from the Asus site nor the absolute latest (June 5th 2018) make any difference.
• Tried unplugging any devices that are not keyboard/mouse/monitor/speakers.
• Tried re-installing Steam (some Steam games have audio, but wanted to try anyway).
• Disabled all sound effects in audio settings.
• Tried low bit rate (16 bit 44khz) and high (24 bit 48 khz) settings.
• Deselected allowing applications to take exclusive control.
• Spatial sound off.
• Quit as many concurrently running application, especially Skype.
• Run Windows Trouble-shooter.
• Checked per-app volume settings (all default).
• Checked in-game audio settings 🙂 But yeah, no audio in games I am running for the first time.
• Checked Steam settings (nothing applicable).
• Checked Sonic Studio (sofware installed by the asus drivers) and made sure all settings are default / no effects).
• Installed older versions of Direct X.
• Disable Windows 10 fast start up.
• SFC /scannow
• Make sure I'm up to date on Windows update.
• Reboot a bunch of times.

None of this appeared to make any difference.

What I did not try yet:

• Reinstall Windows. Was hoping to avoid that, and seeing as how "fresh" this install is, I was hoping it is not necessary.