Granit amp stands are they killing my sound?

From my experience, the worst material is glass. Followed from such stones. You can find a lot of different designs, wood, wood filled with Sand or lead, Plastic (ok, it has a different name which allows to get a higher pricing)...some years ago I tried more or less by accident a Vibraplane below my amp (I used it normally below my turntable) and I closed that chapter immediately. What is made for electron microscopes is ok for High End :-)

"Granit amp stands are they killing my sound?"

Not likely.

The major issue with granite slabs is low frequency vibration activated by either bass frequencies from speakers or seismic type vibration. Placing the granite slabs on suitable cones can minimize the tendency of granite to vibrate. I would not use a granite slab thinner than an inch and a half. I like bluestone slabs from Home Depot because they are thick and inexpensive.

I could imagine a lifeless sound coming from a granite slab ... but suggesting the granite is actually killing the sound could be cause-effect confusion.

Syntax, could you please describe the effect of placing a Vibraplane under your Lamm amps? I have one under my turntable, and I agree with you. It is so effective that I closed that chapter.

I have heavy SS amps sitting directly on my floor. I'd like to try two Vibraplanes under them, but it will be an expensive experiment. Any advice or comments you may have would be appreciated.