Get a suitable HDMI switch that is either IP or IR controlled. Connect that switch to the New 4K HDR TV using the existing HDMI cable (hopefully works)

remove HDMI source connections (Apple TV, Sky etc.) from Beosystem 3 and plug into switch.

Connect SP DIF audio cables from sources into Beosystem 3

Use raspberry Pi to handle switching by intercepting signal from IR eye (still connected to Beosystem 3)

Use serial connection from Beosystem 3 to raspberry PI to signal TV on/off. (if necessary, use a HDMI CEC injector - from Pulse 8 to switch on/off TV- switching the HDMI switch on/off may be enough)

I'll lose the screen curtains, but not much else. The audio will route via the Beosystem 3, and the video via the switch. I've already completed the code for the serial on/off function and HDMI CEC injection, so would just need to map the commands coming from the IR eye to the HDMI switch.

This is well thought, incredible and clever!

I'm impressed, may be in my next iteration (or life) can go that path. Really, sounds clever!

I'd say that just be aware that a CEC injector exists is a great news for anyone interested in TV on/off (I'd imagine most requested feature :) ) I had no idea they existed.

My current plan is to simplify and skip the BS3, and get a TV set with HDMI-ARC connected to the Almando 5.1 Decoder appliance. I'll lose the Beo4 and 7.2 capabilities, but I can drive my current speakers with no other components, has already Rj45 outputs, allows me to input other sources (Sonos Connect, to name one) and it cost less than a BS3; having a BS3 just to process audio is a bit underpinning it.

I was evaluating a dedicated AV processor with pre-amp out but connecting my old PowerLink based speakers to the coax outputs is less lean than with the Almando box, that can drive the on/off switch signal automatically.