Disclaimer: I have zero knowledge of EG in practice.
But, I rather doubt you need to remove the epoxy, and I strongly suspect that trying to do so would let some of the 'granite' fall out, either immediately or some time later. I would simply go diamond wheel for the lot.
Just how well EG on EG would work - I haven't a clue. Sounds bad ... but you can get the surface really shiny smooth. Maybe pressurised lubrication?
Cheers
Roger