you have to go onto 4.46 rex first then use c2d to flash to dex. you can download 4.46 rex from
You must login or register to view this content. and to get to dex follow the tutorial by DEREKTROTTER
You must login or register to view this content. . im pretty much sure you swap over the same as 4.21 and 4.30.2. to answer you original question d-rex is a update for when your already swapped to dex. hope this helps