My Autocom headsets are very sensitive to both the location of the speakers and the microphone. The speakers can be just a little out of position and the volume suffers. This seems to be more true than with the other headsets I own. The mic must be exactly in the right place. Once adjusted properly the Autocom unit, the Pro-7 in my case, works very well.
My Autocomm headsets needed an adapter from Autocomm to work with the GL-1800 headset interface. One is needed for both the rider and passenger. With the adapters in place, the headsets work very well with the stock GL-1800 audio system.
I agree with HardBall that placement of both mic and speakers make a big difference when using these headsets. It may take some time to get it just right, but the headset speakers should stay wherever you put them.