Hi CB,

That is why I suspect the BC2 sends a trigger to the TV. I was especially wondering if it only triggers out in DVD mode and if the trigger signal is usable for other equipment.  

Service manual says it's a 3.5mm female jack where the inner conductor is "IR Out" and the outer conductor is "Not Connected".  The braid shield is labeled as just "Shield".  (I would think that one of the two *should* be GND for the electrical signal corresponding to the IR Out?)

Thank you for checking! 

I was hoping it could be a 12V trigger like on a "normal" system. 

I recently succeeded in getting a true DATALINK connection between my BC2 and MX5500 1988 vintage TV. The CTRL jack did not work as you suggested - I was unable to get any response between the BC2 and MX5500. I reason that is because the CTRL socket is only an output for an IR blaster, and does not receive B&O datalink.  The two are connected via S-Video as suggested by CB to the AV2 sockets on the MX5500.  I created a special cable by breaking open a SCART cable to access the DATA wire (Pin 8) on the BC2. I put a mini plug on that using the SCART cables shield for the ground on the plug. This breakout cable plugs into the SCART socket on the BC2. I now can start the DVD playing by pressing CDV on my Beolink 5000, which turns on both the TV and the BC2. I can also control menus on the DVD via the Beolink 5000 sending commands to the MX5500, which passes them on to the BC2. However, the reverse is not true; if I press DISC on the BC2, it does not turn on the MX5500. 

Remarkable that these two products still integrate.

-Gregg