What are all these metal cans/pods sitting on top of electronics?

This is a form of mass loading, a type of vibration control. Nothing special, just solid mass. Looks better than a phone book, one of the first I tried 30+ years ago. That's how old this is. You can try a book, dive weights https://systems.audiogon.com/systems/8367 lead shot, granite, butcher block, sand bed, literally anything with mass. Not all materials sound the same. 

Look close, you will notice I have done this with a lot of mine. 

I kid you not. They sell bags of rocks. 160. usd. My setup would have taken 1600.00 worth of "ROCKS" to load my speakers properly.

390. each x 5 bags x 2 = 10 bags of rocks for 1600.00 usd.. Nice bags though..  I like the idea, just not the 1600.00. OH They had "Earth Boxes" from 1k - 10k.. NO KIDDING.. Box of dirt.. 10K.
I'll take 5.. Keep the change!

Cabinet material makes a difference too.. My Elixirs are HDF. Go tap on the side walk.. about the same.. The monitor section, 390 lb..

Regards

I would not buy any of these items unless they have undergone cryogenic treatment and quantum cleaning. Be sure their astrological sign is aligned with yours.

Added mass for vibration control, can have a good effect on tubed units and power supplies. Good thing is that you can try and use something without spending a cent.

G

John Darko the youtube reviewer has them on all his equipment.

I would not buy any of these items unless they have undergone cryogenic treatment and quantum cleaning. Be sure their astrological sign is aligned with yours.

And the most important one, sits on the top of his head.

Cheers George