what is the theory behind maple stands and racks?

Interesting thread.
Not sure how the density or hardness of wood types have on vibrational adsorbtion, but in the process of experimenting.
Per the Janka rating for density of hardwoods (steel ball thrown at material) I believe American cherry is 950, Oak 1250, Maple 1350, hardest being Brazilian Cherry 2750

I have some exotic hardwoods I will try under my primaluna 8 tube cd player, that should be revealing device to test.

Just made an entertainment center from 2 layers of 3/4" maple plywood with mdf in the middle, 2" thick. Seems to decouple well between components.
Also Picked up some squash and racketballs to add a poor mans floating layer on top of that by routing a cove bit pit to keep balls in place. Will let you know how it works.

got to get me some of them pure plutonium footers and some extra virgin maple :)

You know its fishing season here in Oregon and even tho its a slow year there's lots of out of work people trying to catch dinner. Well, I went to the local fishermans supply store with the same notion in mind until I came across a bunch of lead weights in the shape of doughnuts called sand dollars. They ranged from 4 to 10 ounces. Naturally my mindset shifted to the potential of for these toxic beautys as audio vibration isolators, so I scooped up 8 of the 6oz weights and some 1.5" cork bobbers and forgot all about fishing.
Back home I went to waste another weekend with obsessive experiments. The guilt soon vanished as I found audio nirvana in a funky configuration that was insightful about vibrations both coming and going from my system. It may be germaine to this discussion.

My Primaluna CD player rests atop 2 inches of maple plywood and mdf. It sounds great but gets little use since hddtv dvr and plasma caught my eyes.
Anyway, If your not familiar with it, the primaluna8 is a tube hybrid cd player with a nice heavy chassis and some beefy rubber feet. I recently swapped the power chord out with a CCAC silver one and rolled the tubes for the first time to some NOS ones that came with it but I had never tried,the improvments were beguiling and compelled me to see what else I was missing out on..
So I started balancing the player on various things. I tryed the dali speaker spikes and their bases. It was an improvement, but the biggest improvement came when I balanced the player on 1.5" smashballs resting on the lead dougnuts. The players big rubber feet have a cavity in the center that somewhat fit the smashballs. The smashballs are quite squishy or resiliant, and so reduced to 1" in height. and the lead sat atop the maple. The lead seemed to act as a heet sink and the air cushion of the ball under stress seemed to insulate the player from ground vibrations coming the other direction.
So long story long, I think you a right, mass matters.
What was cool about this setup was it is a very delicate balancing act and one can see the effects of vibration by simply walking up to the player, the balls would start to roll off balanc.
By the same token the vibrations coming from the player could also move the balls out of alignment. eg I got the balls perfectly aligned under the feet and in the lead doughnuts, turned it on and sat down to listen, After a time the balls would move. I know they are under constant pressure to push back just from being squashed, but the they moved more when a cd was playing.

Bottom line is the improvements were huge with an air cushion separating sources of vibration and the density of the lead as an asorber was astoundingly better than just the balls on the maple itself.