Subwoofer resonance isolation platform vs footers.

Rubber bottle stoppers! I remember those (circa 1955) as little plunger devices to keep the fizz in a 16 oz. Pepsi 'cause I was too young to drink the whole thing.

To the point, I use 4 sorbothane "pucks" under my SVS Ultra13 on a flagstone hearth. It was certainly an audible tweak.

Others swear by an Auralex product called the "sub dude". It's a platform with nothing but rave reviews.

I use threaded Audio Points from Star Sound with my REL Stadium subs. I am on concrete and they still helped. I used the 2" but the 1.5" might even have been better.