I agree with Cmk's take on granite and the dependency on the component, 'table or other, that sits on it.
I'm offering up my experiences here not to counter what others have posted, but rather to share what I tried and what did not work in my case. I would encourage everyone to experiment for themselves to see what really works for them and their system.
I also tried blocks of maple between my table and the granite. I still was not happy with the sound but others may find this works very well for them. So far, I prefer my Galibier's sound when directly on the granite. Just to clarify a bit more, I use a granite slab as well as 3, 4" square blocks of granite that are about 7/16" thick under the table as well to keep the ground wire from being pinched.
But this thread has brought to mind an idea I have not explored, in addition to the aluminum. I should try cocobolo blocks under the table. This wood is much, much more dense than maple and may do better. As with most things, I won't know until I try it.