looking for damping material for my dac

Trying to internally damp my unit (DAC) I need a non conducive metal or XXXX, must he heavy and solid that can be screwed on.
2 pieces L8 X W2 X H2 inches.

Thinking about Slate / Granite / any suggestions??????

I think you would want non magnetic metal or XXXX, but that alone might cause vibrations in other places. I would also damp the inside of the cab with Soundcoat, or Sorbothane, and maybe some Marigo dots on the board, chips, and caps. I mass damp my cabinets on the outside with a brick, shakti, brass, bag of sand, etc. with a piece of damping between the top of cab and weight(except for the sand), i've used bubble wrap in that application also.
Thing you want to put into your DAC is 'conductive foam'.
Long ago an article in Stereophile mentioned experimenting with conductive foam (insulated with card (like 12pack Cola boxes cardboard)under and around all the chips. does work.
Radio Shack sell conductive foam (for IC chip work surface)
And Sorbothane rubber is the stuff for cabinet resonances