Ableton Link DDj-400 and DJS-1000

Hello experts

I have Ableton live running and link the rekordbox to it. Connection the DJS-1000 for bpm synch works some kind when the DDJ is not connected, but the bpm on the DJS ist jumping around +/- 10 prety fast (through the linked BPM in rekordbox is static).

When I am connecting a DJS 400 th the same pc for controlling rekordbox, the link does not work anymore. And: now the play buttons on the DDJ do start/stop both decks at the same time - so it seams that midi channels are missmatched?

Any help possible? Maybe a computer / driver problem?

Thanks a lot.