On your original question: Something like an Alesis Micro Gate might be a good starting point. One of these in a "Y" connection with your main signal chain could open the gate to the second branch of the "Y" at a certain signal level. It wouldn't suppress your primary signal chain, but the secondary branch would be silent until the signal level threshold is hit, and return to silence when the level falls back below the gate threshold. Or, you could run a separate signal in/out of the Micro Gate and trigger it with your primary signal source level. As a bonus, they're inexpensive and stereo, the two sides trigger together but signals are independent.
Manual: https://ia802808.us.archive.org/5/items/synthmanual-alesis-micro-series-owners-manual/alesismicroseriesownersmanual.pdf
Manual: https://ia802808.us.archive.org/5/items/synthmanual-alesis-micro-series-owners-manual/alesismicroseriesownersmanual.pdf