[Warner306]

We're cross posting, LoL.  It wasn't a power outage issue here eliminating the AVR settings retention or registry corruption upon BSOD eliminating the HTPC.  It was simply a little overlooked nVidia audio driver bug introduced for some reason and every subsequent driver release since inception.  I doubt they are aware of it.  Some posts back, I listed my results testing drivers from 385.28 and up.  Either the audio was ok but the video wasn't or vice versa.  I forget the exact release that introduced it, but it's listed in that post.  This is the main reason I cannot and do not use any of the newer drivers.  I have too many TV seasons compressed to a dribble including AAC audio that I demand play multichannel.  The biggest problem is multichannel audio in video mode vs playable web video.  I simply refuse to manually change 7.1 to stereo and vice versa depending on source.  That to me is ridiculous.  You say your fix using newer driver(s) is to select the AVR as your audio device in Windows audio settings I assume.  The only devices I can select are video card ports and they are all controlled by nVidia audio.  How are you selecting anything different?  If you mean KODI internal player, you should be able to set audio as stereo which will reveal a hidden AC3 setting you can enable and then set back to 5.1 or 7.1 and still use Wasapi.  Are you able to select the Windows audio 5.1 or 7.1 setting AND play a youtube video without manually changing anything?  I am on the older driver.  Sorry to hear your trials tribulations after your outage.  You went through a lot trying to get back what you had......

 I'm not sure if we have the same issue or not. Windows should default to stereo even if you select 5.1 or 7.1 in the Windows sound configuration wizard. It was stuck in multichannel after playing a multichannel source. Any upconversion of the stereo source should be done by the AVR unless specified by the media player or decoder. So, I can play a stereo source from a video add-on and it won't playback in 5.1; it is stereo and upconverted to Pro Logic II by the AVR. 

I select the AVR as the audio device, which is the device connected to the HDMI port of the GPU. Selecting Nvidia (High Definition Audio) is also a device connected to the same HDMI port, but it specifies the graphics card as the device rather than the AVR. These two devices corrected my issue by overwriting the error caused with the AVR device. The Nvidia (High Definition Audio) device seemed to overwrite the settings for AVR connected to the same HDMI port.

If uninstalling and reinstalling a different driver corrects your problem, then we don't have the same issue, as this did nothing for me. I thought you might be using a system restore, instead, which might mean something similar is stuck in Windows.