What are the things is the photo?

Herbie's Grounding Bases.

....

And I just noticed I somehow thought the OP was morphsci. Humble groveling apologies.

No apologies necessary on this end. I just wish I had a speaker isolation problem to tackle, but not for a few more years.

Herbie's Grounding Bases.

FWIW, I've always liked Herbie's stuff I've tried. I recently bought Threaded Stud Gliders for my speakers and they've made moving/making adjustments so much easier on the hardwood floor. They also made the speaker bit more stable than with the spikes, which is a plus in my book.

What's wrong with using marbles? (if you have carpet, and yes I used them, though I am not sure if their was an audible difference).

Have you lost your marbles?

Bonnie found steel and zirconia balls here:

Bearing Balls:Ceramic,Miniature Ball Bearings