I'm with Siramic on this one.
I'd seriously go with the Marble guys, they know their stuff!
I'd get him in to do the floor, and then you can 'see' how it's done and ask questions whilst on site. Marble is fickle stuff and you could easily make a floor worse by a poor product selection.
I've been tiling for years, and i'd much rather give this sort of job over to the experienced chaps.