I found the folder with Amplitube 5, and I placed it in "Locations" under Studio One/Options. It sits on the list right below PreSonus
Studio One 5 still does not find it. When I click on "Files" in the browser, I see the path to the folder, but when I click on "Vendors," it does not appear.
I have still not found a way to use Amplitube in Studio One 5.