Sound problem is most likely linked with issues in the cables. Here are a couple of things you can do:
1. Make sure all your cables are plugged in securely including the microphone and MixAmp.
2. Try plugging your headset into a different audio source and see if the problem still exists. You can try it with an mp3 player or a stereo.
3. Replace the Quick Disconnect cable that you are currently using with another provided along with the headset.
Hope that helps!