subwoofer buzz - how to eliminate it

Bingo!

You might also consider moving sub to a less excitable location in the space.

“More rubber”? I definitely had a chuckle there.

It is placed on a wooden floor on rubber footers.

So why is it 'vibrating like it wants to fall apart' straight out of the box.

It's obviously faulty.  Take it back.

These get great reviews and are very reasonably priced. I'm thinking of getting some.

https://www.svsound.com/products/soundpath-subwoofer-isolation-system

I have the svs ones on my living room sub. Without it pictures on the wall would rattle with it no rattle.