I had already given a thought the workaround through modifiers, but hoped to find an easier solution.
Nevertheless, I just spent about 6 hours mapping the sh** out of my K2 and finally: it works!
@BradCee: It might interest you, that you only need one modifier to control for both decks A and B.
Example (Sync button):
One more question for the experts: what's your experience with the "blend" option in traktor. Is it really as arbitrary, as it seems? I ran into a few problems with the LED feedback; sometimes enabling the "blend" option solved the problem, sometimes it didn't, although the command structure was exactly the same?! Weird..Code:mod=0 -> sync neither A nor B mod=1 -> sync button A mod=2 -> sync button B mod=3 -> sync button A and B enable sync A (if mod=0) -> mod=1 enable sync B (if mod=0) -> mod=2 enable sync A (if mod=2) -> mod=3 enable sync B (if mod=1) -> mod=3 disable sync A (if mod=1) -> mod=0 disable sync A (if mod=3) -> mod=2 disable sync B (if mod=2) -> mod=0 disable sync B (if mod=3) -> mod=1