Sorbathane under granite slabs for speaker bases?

Always good to experiment, ahahitoro.  Plain granite now doesn't eliminate the possibility of later trying some wood in between.  

To answer your question...yes, I use the spikes as well.  With the Silverline Preludes, I use the spikes they supply though have installed those little dimpled discs to keep the spike from digging into the wood.  With the Forests, they have a "ball & claw" arrangement for coupling.  The balls rest directly on the wood.

Well, I have a thoery that works for me. How you implement it is up to you.

1. Minimize surface area contact with floor, furniture, etc.
2. Minimize opportunity for speaker to move, often by adding mass.

The reactive force of the woofer motor can cause enough motion to distort the sound, or vibrate against the floor, Minimize that by any means necessary.

At one time, I had a pair of floor standing speakers on a 1 inch thick slab of black granite.  It not only tightened up the bass, but removed a slight smear in the midrange.  I placed them directly on the carpet with the speakers with spikes installed on top.  I used the cups for the spikes to fit into. 

Send a message to Robert @ Herbie's with your specific question, he will get back to you quickly.

My floors are raised wood. I  had a hell of a time getting the speakers to sound right.

 I tried just spiking them through the carpet and into the wood floors. Undefined  bass. 

Then I tried them spiked to granite bases.  Improved mids and highs. No bass. 

Finally, I bought a pair of Maple Shade unfinished maple platforms. I spiked the platforms to the floor through the carpet, then spiked the speakers to the maple platforms. Walla! Done. 

Double click on my icon, then double click again to see the Maple platforms under the speakers. 

Frank