As per the reference post, I did
apt update && apt install libasound2=1.2.2-2.1 libasound2-data=1.2.2-2.1 libatopology2=1.2.2-2.1, and nothing changed. After reboot, the only available audio source is the digital SPDIF, and when I issue the command to create the new sink for analog stereo, a notice appears saying the new sink has been found, but I still can't use it, and the whine from the speakers persists, though I only just noticed that the speakers begin whining as soon as the machine powers up - even before the OS is loaded... Hardware issue maybe? Also, the HDMI Audio on the AMD card still doesn't appear.
Anything else will have to wait for tomorrow, as I have to get to work shortly after posting this. I really appreciate your help so far!