I did something similar over the past few days with my Berkeleys. The Berkleys have M8 nuts but not strong enough for the M8 Superspikes I got recently. So got some hardwood (Utile) and fixed M8 inserts into the hardwood. As expected the sound tightened up nicely with a clearer focus, as well as raising the speakers to a more useful height. Did think of granite but not sure how I would fix M8 inserts into the granite.
Current: [P20] Roon/Tidal > Custom PC> Chevron Paradox NDF16 > Phast Pre > Neuro. 686 > Tannoy Berkley (RFC tweaks)