Offizieller Kommentar
@Matthew > Currently neither the RX2 nor rekordbox can transmit that data, but another device which could translate the audio signal to determine the tempo (such as a DJM) and then output that information as a MIDI signal (or in the case of the DJM; ProDJ Link) would be the solution. Obviously not ideal, but one of the few work-arounds available at this time.
We're expecting future updates to rekordbox will include Ableton Link and possibly a direct integration for a DJS-1000 so it can sync and be used in performance.
Thanks!