That experience with the system restore not fixing it is disturbing. I don't think there's any way for an update to damage hardware, but it suggests it's modifying something that neither system restores nor repair installs can reach.
My reason for not thinking it damaged the sound chip is, as I mentioned earlier, I followed up by installing a USB DAC that wasn't even plugged in when I did the update. Windows still says no sound devices are loaded, even though I know the DAC is working because programs like Foobar, which allow you to access audio hardware via its own ASIO interface rather than through the Windows audio system itself, can not only locate the DAC but actually play music through it, even as Windows is saying no audio devices exist. And, as I pointed out earlier in this thread, for each of these devices, Device Manager/Properties/Events gives a "not migrated due to partial or ambiguous match" error. This suggests to me that, somehow, the update messed up something in Windows that causes it, when it goes through the devices/drivers to enumerate audio sources, to see properly working devices/drivers but flags them as having a problem. And, whatever it may be doing, it's doing it in a way that neither rolling back via System Restore nor doing a repair install can correct. Unfortunately, I know zero about the internals of Windows, so I can't suggest what might cause such an event to happen, but I'd be curious to bring up the matter with members of the team that coded the audio subsystem of Windows, because I can't see how something like that couldn't be tracked down and fixed in a future update.
In the meantime, as I said above, I'm going to do a clean install to a replacement boot drive, put all the updates on it, and see if it works this time. If so, I'll move on from there. If not...we'll see.