Looking at the pinout of the headsets, I would probably check the 'mic -' path, and how that relates to the PTT switch. I would use a multimeter set so that it will read the 2.2kohm impedance referenced in the 3rd pdf linked to. Put one probe on the mic +, and then use the other probe on the 'PTT' wire to see if you get a reading, and then on the 'Ground' wire checking the same. With the probe on the PTT line, you'll probably need to press the button on the headset to actually get a reading. (I've seen this before when fixing Motorola headsets with the dual 2.5mm and 3.5mm jack connectors for newer handsets. The PTT switch is a push to make switch to compete the microphone circuit.) My hunch is the the ground wire is just for the speaker, and the PTT wire is actually the mic -. If the latter is the case, you will need to decide if you bypass the PTT switch in the headset so the mic is always live, or see if it works ok as a PTT with the tech pro system. Depending on the overall headphone level and how the volume control on the comms system behaves, you may also need a resister in series on the speaker circuit. From memory the standard Techpro headsets are 200 ohm for the microphone and 400ohm for the earphone. With those headsets being 32ohms, the volume might be a bit loud in the ears, or may only give you a tiny adjustment before it becomes very loud. Also the headsets look like they will be in mono, so speaker + connects to either pin 4 or 5 on the camera cradle (I suspect pin 4 and pin 5 is not connected.) I'll defer to Sandall's post on the need for power, as the 1.5v operating volume for the microphone is something I've never had to worry around in my dealings with comms systems.