Maybe you needed to reboot your machine after running the installer.
Can you try this? Move the two files from MB's plugins folder to somewhere else. And reboot your machine and see if Milkdrop works without the two files in the plugins folder.
If it's still not working, instructions will need to be updated.
Just to clarify, on the new PC, I have NOT yet run the "directx.exe" from the "DirectX End-User Runtime Web Installer" link in the first Post,
The files "D3DX9_43.dll" and "D3DCompiler_47.dll" already exist in "C:\Windows\System32" folder.
On the new PC, Milkdrop just showed a blank screen and crashed after a few seconds.
I didn't do anything over the weekend, then when I read about ONLY moving "D3DX9_43.dll" and "D3DCompiler_47.dll" to "Musicbee\Plugins", today, and Milkdrop worked ok after a reboot.
In the 2 older laptops, both Win 10 pro, if that makes any difference, "C:\windows\System32" has ONLY has the "D3DX9_43.dll" and NOT "D3DCompiler_47.dll", and they both worked fine with Milkdrop.
I'm sure you can understand that I'm nervous about running the DX now as all working just fine, but more than happy to to REMOVE "D3DX9_43.dll" and "D3DCompiler_47.dll" out of "Musicbee\Plugins" to see what happens...
I'll report back shortly - Regards: Freddy