I found an easier way to make the LoopMash, Spector and Mystic factory presets available for C12.
- Copy the vstsound files from the folder
C:\Program Files\Steinberg\Cubase 11\VST Sound
in a new subfolder of your vstsound content folder, e.g.
V:\Steinberg\VST Sound\Cubase11 - Rename the files so that they do not appear twice in the system, e.g.
“FCP_SMT_004_Cubase11.vstsound” - Register the copied vstsound files in the new location with the Steinberg Library Manager
- Start Cubase 12
- Rescan the vstsound folders in the mediabay
That’s it 
Edit: It seems to be even easier to make the factory presets of the 4 “old” synths available in C12:
You don’t have to copy anything, rename anything.
Just double-click one of the vstsound files in the folder
C:\Program Files\Steinberg\Cubase 11\VST Sound,
then all vstsound files in that folder will be registered in the Library Manager.
And you can even see what function these files have:
