Alex' suggestion did the trick. For anyone following this thread, I've tried Option 2 for BV8 and 0 for the Beosys6500. That worked, though it gave me no feedback to the Beolink 5000 from the Beosystem.
I then tried to trick it and got tricked in return, the result being double inputs. (BV8 Option 2/Beosys6500 Option 4).
Alex' advice of using Option 1 for the BV8 is the solution. The Beosystem 6500 is in Option 4, and the Beolink 5000 in One-Way mode for AV and Two-Way for Audio.
I now get feedback to the Beolink from the Beosystem, I have full control of the BV8, and I just channel the sound from the Beosystem through the BV8 speakers by using the A/V button. For a moment I thought all was not perfection, as I tried muting the sound from the Beosystem, and while the Beolink was showing a mute being carried out, there was still sound.
Hmmm ...
Turns out you have to use the A/V button then, to return control to the BV8, and then mute. Perfecto!
And yes - option programming B&O is tricky.
Beosystem 6500 (Option 4) connected to the BV8 (Option 1) through a 1611 Converter box that connects to the masterlink of the BeoVision. Using the BeoVision speakers.
And to those who asked above regarding FORMAT and using Picture on the Beolink 5000. No, I can't get that to work, have to use the Beo4 - and it's kind of silly that the BV8 doesn't just stick with the previous formatting, requiring me to redo it every time.