As long as the Epoxy was WELL ADHERED to the floor you can attach DIRECTLY to the epoxy. I would do a test patch and let sit for 2-3 weeks. IF you are going to have a failure involving epoxy adhesion it will show up generally within that time. if after a month you see no adhesion problems Go for it.
IF you see delamination, Check with your tile company to see if they have any alternate types of glue. Depending on the actual polymer the top seal is made of some adhesives will react differently with them.
if you are still having problems PM me and I may have some additional solutions.