Being new to all this I went & had a read of a couple of articles when I saw this thread so I would have a better understanding of what it was all about.
I could be wrong (often am) but from what I picked up what they are trying to achieve is not the same as filling a machine to increase it's weight or help with vibration dampening. Haven't read the long thread on their forum but I think that is why they are still theorizing & testing different mixes.