Fastrack is a noisy track. At best, you can only reduce that tendancy somewhat. it will never be a quiet as Atlas, Gargraves, etc.
Use of any sound-reducing material - cork, foam-board, acoustic tile, rubber, etc., is preferable to nothing at all - and there really isn't that much difference in the effect any of them have - they all work pretty much as well as one another. I'd use whatever you think you can most easily use.
A couple of years ago there were long, detailed - very detailed, discussions by others here as well as me on additional measures to take to "quiet-down" the white noise Fastrack makes as well as its tendancy to reverberate and amplify that noise. Filling the under side with expanding foam, and not using any fasterners, were among the tips. Those measures made as much or more impact on Fastrack noise as the substrate material you pick. You might do a search on this site for those if you want . .