OK this is what I did:
So since there are only 3 wires in the BS2-IR-cable: yellow, green, and brown, I only connected these three as shown in the Beolink Passive manual.
This caused some problems, the Beosystem 2 was changing the channels sometimes accidentaly, very strange.
changed the wires now so it matches the picture that matbkk posted, hope it will solve that problems (for the moment it does, but you never know...)