What is the perferred material for a TT shelf?

It's always good to hear DIY solutions...

This will only set you back $40 or so give it a try; I use this on my Pro-Ject Xtension 10 and I'm happy with the results and it was easy and cheap.

IKEA Lamplig bamboo cutting board. The board has a grove on one side so I have that side facing down. $14.99 plus shipping.

Between the cutting board and my rack I use 4 RTOM Moongel Dampening Gels. I place the gel pads to the inside edge of the grove noted above; not in the grove but pass the grove. If you live near a Guitar Center or any drum shop they sell the Moongel there. Us drummers have been using this stuff for years. Package with six pads is $7.

This simple cheap tweak works great on all components as well. 

I have a DIY rack from three 3 1/2 in butcher block. The block is manufactured by patching together about 60-80 squares of maple with the grain running in different directions. My thinking, if you can call it that, is that the different orientations would preclude linearity in the wood thus reducing vibrations. I ran threaded brass rod capped with acorn nuts on each end. It sits on Herbies isolation footers. Seems to work great. 

I went with a 1.125" of solid cherry, Definite improvement over what I had.

Get a used Symposium Ultra on Audiogon for best sound.