I put in a very similar system in my kitchen, but used no cork or any other insulation under the tile. My install included wire in thinset over subfloor, Ditramat over the subfloor, then stone over the Ditramat. I did insulate the basement ceiling using foil covered bubble insulation (not sure exactlly what it is called, comes in long rolls at HD), but I am not sure it really makes the floor above any warmer. I will say the kitchen floor feels great in the winter. Also, the foil based bubble wrap keeps the aliens from reading my thoughts when I am working in the basement, so I guess that is a plus.