[bixby]

Great bamboo source is Ikea:
http://www.ikea.com/us/en/catalog/products/00233429/

$14 for the thick one and less for thinner.  I have experimented considerably with them and they are good, just depends on what flavor you are after.  I have combined with rack MDF shelves or separated by Herbies Tenderfeet.

The changes many of the materials can bring to the overall sound of a speaker based setup is amazing.  Bigger changes can be had with different footers on a rack than by switching dacs in many cases.

I have moved on to a quasi constrained layer damping footer using poplar.

EDIT:  Oh and if you have not tried it, go isolation, on your speaker monitors and stands like Herbies suggests.  Decades of spike use has been defeated, haha.

[simoon]

Just because something is dense, stiff, heavy, thick, etc, does not mean it will be good for audio platforms.

The most important attributes are how well damped the material is, and a what frequency it resonates at.

Granite and slate are both very close in these attributes, and neither is very good.

[Bob2]

Granite and slate are both very close in these attributes, and neither is very good.

I disagree. I have a 3 inch thick granite surface plate, 96.5 lbs.,  under my turntable and there is zero transference of vibrations.
Large mass at the volume levels I listen to, 95db>  at times reveal no effect on turntable performance. Turntable on my Salamander rack without the granite had the tone arm vibrating and at times bouncing..

[sunnydaze]

For several years I used the same exact granite surface plate (Grizzly) under my Townshend Rock Mk3 table and heard no detriment.   Matter of fact, it sounded quite good.

BTW, beautiful setup Bob2!      What is it?