Some David Clark headset models have the hi-lo switch. They also have a printed circuit card inside, and it's not a matter of a simple switch, you also must have the circuitry. Perhaps DC will sell the circuit card separately, although I've never tried to buy one. DC does have excellent customer service, though, so it's worth a try. I'm also unsure which microphone the switching DC headset uses, but I suspect you'll need to use the same type. A dynamic mike is normally high-impedance, along with most civilian mikes. In the US, only the military normally uses low-impedance electronics, and every civilian aircraft I've been in uses high-impedance.