The venerable 8000a can be split into pre and power amps relatively easily. Sockets are already provided, so it’s a case of removing two buffer resistors to remove the internal link between pre and power amps and adding two input caps to block any DC going to the power amps. It is also relatively easy to plumb in a relay in parallel with. The main delay circuit to add an 8sec mute to the pre out. Finding a relay that fitted the circuit board proved impossible, so I had to plumb in a larger relay. You also have to install the power for the relay from the main delay circuit.