I can really see the image trying to come through. But given the small difference between darkest and lightest on the material. I think a lot is going to depend on the composition of the granite and how it is finished. Did LaserSketch have any suggested settings?
also it can be done at least on some black tiles.
Maybe compare your settings to those in this thread: Engraving Black Granite tile
I am afraid the composition of your granite is coming a lot closer to @rbtdanforth but coming from laserSketch and comparing to their examples it really looks like you should have better results.