I am using enhancer pro. I like the look of the enhancer because it darkens the color of the travertine. I have used it on part of the house and it looks great, but I was told that if you polished the travertine, it will give it a more "industrial" professional looking floor (the finish looks more like granite or marble).
I guess I could apply your idea and use and stone enhancer first, then use the high gloss sealer as you have suggested. Thanks for the idea