If you're on a Mac you have to use the VST version instead of the AU version!
(I had a similar problem with Antares Harmony Engine not showing up in the Input selection box of an Instrument Track until I found out that I've to use the VST...)
I'd leave the soundset folder itself where it is. Just move the file that are contained in that folder to another location.
I don't know Cubase at all but Studio One can import Steinberg Cubase Tracks Archives (.xml). So try to save your songs from within Cubase in this format and then import them into Studio One. (And make sure to backup all your songs in the original format so that you can always returns to these versions ).