I second the plinth idea with the addition of 3" brass footers under the plinth. It will be a tough job getting these up on the plinths, however.
I have this setup on my B&W 803ds, with 2" brass footers between the speaker and the plinth, and 3" brass footers between the 3.5" maple plinth and the wood floor. It was a real b*tch getting the speakers up on the plinth (and they are nowhere near as heavy as yours) and a bit tricky to balance as I am using only three footers under the plinth (tripod arrangement). But the sound improvement was worth it.
I have this setup on my B&W 803ds, with 2" brass footers between the speaker and the plinth, and 3" brass footers between the 3.5" maple plinth and the wood floor. It was a real b*tch getting the speakers up on the plinth (and they are nowhere near as heavy as yours) and a bit tricky to balance as I am using only three footers under the plinth (tripod arrangement). But the sound improvement was worth it.