I knows these are long posts but I'm trying to provide as much detail as I can - I really need to resolve this, especially if I can't stay on an older working version anymore without getting forced updates an hour or two later
Not sure if this makes a difference, but the driver update leaves a MaxxAudio installer file on the drive, which seems to install a different version of the control panel if you run it manually. It looks different to the one that the driver actually installs automatically
The MaxxAudio control panel that's installed after you update the driver is the one I've always seen - with MaxxBass and Details knobs on the left, and a Width knob and Midnight button if you're on Internal speakers.
But there's an installer for a different version on the drive at
C:\Program Files\Realtek\Audio\HDA\Waves\Maxx Audio Installer (x64).msi
and the folder was created around the same time the driver was installed, so I assume it's part of the installation. If I run that, there's a Repair option (which has no effect I can see) and a Remove one, which uninstalls MaxxAudio. If I do that and run the installer again, I get an Install option for "MaxxAudio for Ultrabook" - this claims to fail with "Icorrect permissions, aborting installation" (with the typo) but it does install v22.214.171.124 of MaxxAudio (which is the same version number as the one the driver installs automatically).
This version has a couple of extra buttons at the bottom left, Reduce Noise and Revive under a label marked S*treaming (I'm not allowed to type that word here for some reason??). There's also a message on the right above the EQ that says "Current default playback device is not supported". The actual on/off switch at the top left is disabled - I can't turn MaxxAudio on
There's another copy of this x64 .msi file at
C:\Program Files (x86)\Realtek\Audio\Waves (dated 19/10/2018)
along with an x86 .msi file. By the date I'm assuming this one got installed with the last version of the Realtek driver, which also broke MaxxAudio, which is why it seems suspicious to me - are the recent drivers supposed to be using these newer-looking versions, but failing to install them properly? (The actual x64 .msi file is the same version and creation date in both folders, 2.7.9434.5 and dated 18/10/2018 05:19 - I'm in the UK if these timestamps matter)