Your choices should be focused on the type of track you're using. If you're trying to mitigate the sounds of Fastrack most of the niose comes from the resonating of the the plastic roadbed and without filling the void inside of it you're not going to quiet it down with any solid surface including quiet brace.
The best sound mitigation for fastrack is floating it over carpet. Quietbrace is good for traditional tubular and solid rail track:Lionel, Gargraves, Atlas...
