Unfortunately, D2:ED saves are not compatible with DKS (there were too many changes made to enemy placement, loot, etc). You will be able to start a new level 35 character at the beginning of the add-on content, though, if you don't want to start over with a new character, or would just like to do the add-on first.
On the PC FoV does maintain compatibility with D2:ED saves, but it will not be released by itself on the Xbox (it is too large for DLC, and Larian could not get a publisher for just the add-on).
