FWIW - I got checksum errors a couple times (annoying)… so I simply took the missing .vstsound files from the MAC download… located, after install, in ~Library/Application Support/Steinberg/Content/The Grand 3/VST Sound.
I can’t remember if the files are visible prior to install (once you mount the .dmg), but my guess is they are…
This, of course, requires that you have a MAC.