I have two questions:
When you use a mixer like the Mixamp, it is mixing voice and game sound, right? Is the voice the other player's voice in the game? Or is it mixing the game sound with your own voice? Does this device take the microphone input as well? Looking at the Mixamp Quick Start Guide, i don't see a mic input. If it doesn't have one, then I guess you plug your mic directly into the PC bypassing the Mixamp all together? I guess its intended for headphones instead of headsets with a built in mic if so.
Secondly, do any PC video games create a virtual Dolby-like surround effect for stereo headphones? Battlefield 4, for example, has a surround setting in the Audio options that is available even with headphones selected. Or maybe the headphones is simply an EQ preset.