MAny thanks for this - I have made some progress but some issues remain or have returned:
I exchanged the HDMI-to-DVI-D cable for a dual link DVI cable and a HDMI-to-DVI adapter that sits on the Apple TV HDMI socket. I also used a simple component cable in order to have the audio, too.
Then I realised that I had mistakenly configured the AV3 port for PC input on the BV7. I changed that to AV4, and - bingo! Everything worked just fine!
Now the bad news: after disconnecting the whole system again from power supply in order to install all the wires properly and then reconnecting power again, there is NO video signal anymore! Strangely enough, the audio works ... Any clues with this?
I will definitely try to use composite video rather than HDMI/DVI. I am however unsure as to whether this will solve my issue.
Comments and help are welcome!