Official comment
I tested this out, and unfortunately since the DDJ-RB and DJM-250MK2 are designed to provide a similar function (audio mix), they fight for control. Even in the best-case scenario where I was able to get both devices to exist within rekordbox and not disconnect constantly, without monkeying around with external ASIO software, your audio outputs would be limited to 3 decks, with the 3rd deck coming through the AUX input.
It's not a conventional setup and is more pain than it's worth. Sorry.
