[brazen1]

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. 

 Let me give you a little background to help you understand..... to help me perhaps regarding this new driver vs old driver (bug).  You probably understand I'm an automation nut job.  I want my environment to perform as if I'm an invalid confined to a bed or couch with nothing except a remote in my hand when I want to watch or listen to something on my TV.  This means turning on all the equipment and having all that equipment adjust themselves to all the relative settings for the activity I've selected from that remote with the press of one button.  Once everything is fired up, I want to scan my library, select something, and do nothing else except watch it.  When finished, I want to press one button and turn it all off.  Much of this is accomplished in software but some requires additional code and I share some of my techniques here showing how I obtained my goal.

From that same bed or couch, another activity would be using my computer, which is the same HTPC.  Again, from on to off and everything in between.  I will however add a mouse and keyboard and not only the remote.  I don't want to have to change any settings for anything from activity to activity.  I've noticed (using the newer drivers) a negative affect.  I can manually fix it.  I don't want to manual anything I shouldn't have to.  I could automate the fix.  I don't want to fix anything a driver broke that used to work.  I'd rather wait and see if the driver gets fixed.  Until then, I use a driver prior to breaking.  This old driver does everything I want it to.  Now I see a new driver has improved audio/video sync to lessen dropped frames from every few minutes to every 10 minutes or so.  I would like that improvement but it would be at the cost of reintroducing the audio bug that has not been addressed.  I will continue using the old driver.  I'm not sensitive to a frame drop every few minutes as much as the audio bug.

When I presented the audio bug, I was told not to turn off my AVR.  When I use my HTPC for movies, of course I use my AVR.  When I'm just using my HTPC for computing, I don't use the AVR.  It is off and not in standby (and why should it be), just HDMI passing through.  I use my TV speakers.  Being the automation nut job I am, the volume is controlled by the remote and distinguishes between controlling the TV volume or the AVR volume depending the activity.  With all this in mind (sorry) here is the problem and perhaps you can confirm or deny?

Using your newer driver, with the AVR on - You are achieving all audio formats from all players (MPC, PDVD, DVDFab, KODI, etc.)  DTS:X, Atmos, DTS:HDMA, AAC, AC3, etc.  You can use Wasapi with no conversions letting the players and filters feed your AVR which displays all the formats for what they are - non decoded Hi Def sent exclusively to your AVR.

Now, turn your AVR off and go play a youtube video.  Don't forget to turn your TV speakers up (but this won't matter).  What happens?