Headphone Audio Issue

Hello,

For FSX and many other games, I am using the EACH G2000 headset. I am pretty sure it has 5.1 audio --> front left and right, center(basically subwoofer), and rear left and right pairs. When in fsx, the sound of anything behind the cockpit is very faint, mainly the engines. However, when I look around in the cockpit and look backwards, the engines become loud. I need to know how to change this because obviously when looking forwards you would still hear a loud engine sound. I can fix it by putting the speaker mode on Stereo but the audio quality rapidly deteriorates. Leaving it on 5.1 works better.

Help!