Welcome to the forum, Joel.
I'm not a natural stone expert, but I know enough to be dangerous.
One of the advantages of epoxy grout is low maintenance. I'm not sure there is much advantage to having a grout that requires less maintenance than your tile though. I believe that your tile will need to be periodically sealed, so I would use regular grout. If all
your grout lines are 1/8" or less, you can use unsanded grout. Otherwise, use sanded.