Was rading a bit about damping and found this power point presentation about a manufacturing method and material called iCTech. Looks like a cast iron frame filled with something similar to epoxy/concrete and aggregate.
This is not a scientific paper, but it claims much better damping and stiffness to weight rateio than regular cast iron. If this is true then filling steel beems with epoxy granite should help on both stiffness and damping also. Although if it is cost effective is another question
What do you think?