The regular PC audio is "Realtek". NVIDIA is for HDMI audio.
What configuration do you usually use that is causing the problem? Do you have Realtek enabled and set as the Default "Recording" device? (and "Speakers" as default playback device).
I always have a displayport cable connected to my display that I sometimes use for audio but usually I have my G35 headset connected and it is set as recording and playback device.
Also the Nvidia HD Audio Driver seems to get reinstalled after each reboot.
I think I tried unplugging the headset and using the HD audio driver (my display) as the playback device and the problem occured too.
You can disable devices in the Device Manager, e.g. the NVIDIA audio.
With the USB headset, that does not use the PC audio (or HDMI audio) as it takes digital audio directly and converts it to (hearable) audio in the headset.
If you are not using the display port, remove the cable to avoid any potential issues.
Yes, use DisplayPort (cable and socket) for monitor.
If you have external analog speakers, they should be connected to the back of the Aurora-R7 ... NOT the monitor.
As Fireberd says ... USB Headsets have their own "sound card" in their cable, and also their own drivers. I suggest you keep them dis-connected during trouble-shooting this because they are un-related and just complicate things.