Iirc you need to switch the Mic in the headset to an "Electrical Condenser Microphone" to make it work. There was an "how to" somwhere on dragonredairsoft.
€dit: Found it ....
Attention: If you use real steel military headset, if you can hear but not seem transimitting, please try change the headset's electrodynamic microphone(moving coil microphone)to Electret condenser microphone(electret microphone)
http://www.dragonredairsoft.com/cata...cts/modAll.jpg