How can I make my new Travertine tiles more shiny?

The tiles are of the honed and filled type and have yet to be sealed with an impregnator. The majority of the tiles are in a wc room - walls and floor with (electric underfloor heating) and some in bathroom (floor with elec underfloor heating) and around basin and bath area. I have tried sanding a spare tile with 200/400/800 and 1200 paper with water but can hardly get any sheen on it at all. I am looking for a semi-gloss to gloss finish. Would like to use a low maintenance sealer ie reapplying no less than every 2-5 years if poss. If it requires extra polish on top of that then am willing to apply that more often. Thanks!