So I know this is an old thread but I'll still post in case someone else needs help but yesYes, there is a type of pad used exclusively for tiling over a concrete floor or over uneven subfloor. The pad stops cracks in the concrete from telegraphing through and eventually poppingcausing tiles to pop up the tile or causing thehe grout to prematureprematurely erode away. A cork pad is just 1 type of padding material used for this type of application. The pad is first thin setbonded to the sub-floor with thinset, then thin set on top of the pad then tile on topis laid in a thinset bed atop the pad.
Epoxy grout does not "give". Epoxy grout is exactly what it sounds like. It's a chemical reaction between two chemicals with, and most companies use a Kevlar-type materialaramid fibers added in the mixture for strength that's almost indestructible. You have to work very fast with epoxy grout: you have about a 20 min working time after mixing it and the more it's mixed the shorter the working time gets. Plain epoxy grout is smooth, but you can get a sanded version. You literally have to grind out epoxy grout with like a Dremel, while normal grout is a variation of Portland cement that can be scraped out with a knife.