For those who tried just granite alone and found it unfavourable, it really depends on the TT design. Some TT already have some sort of absorption/deflection designed into the TT's footers. You really have to see the total package.
Granite on its own would generally "sound" hard, cold, because it reduces low frequency vibration, but rings some where in the upper frequencies, unless it is dampened by the TT's own absorption. However, granite is good for reducing ground borne vibrations, especially if your system is full range.
The solution then is to combine the benefits of granite with those of a wood based platform. The granite below to cancel out vibrations from below, the wood/semi-hard composites to absorb vibrations from the TT itself.
I'm using the DH squares above granite and it works wonderfully.