You say that the epoxy can be buffed, so I suggest buffing it on a regular basis with a small buffing machine. The ones sold for household use are hard to find these days. Alternatively you could have a janitorial supply company come in & buff the floor every month or so. Once you've got the scratches out you could apply a buffable paste wax (say Johnson's Paste Wax) to the floor & buff it occasionally. Or you could apply Future (from the grocery store) or Step Saver & when this marks up remove and/or reapply. It sounds like the big problem is the hard plastic wheels you have on your chairs. An option might be to remove these castors & intall felt gliders on the bottoms of the chair legs.