bb,
It depends entirely on the aircraft intercom fit. Even within the same fleet these may be very different. For example, some of the S76s I have flown have had DIN plugs, others have standard NATO plugs, but have been either high or low impedance. I currently fly in S76A++s with low impedance systems and S76C+s with high impedance systems. Ideally you should get a headset with switchable impedance, such as some David Clarks; or changeable microphones, such as BOSE.