Are you use direct sound from the game or is it being re-encoded.
A clear way to test this is get in a GV battle and listen for start ups. Better yet set in the tower and as planes fly by they will not sound correct 
I use mitsu's, tb's, rangers and sketchworks.  I switch them around every month or two.  in the tower, I can hear the direction of the airplane before I see the plane.
I dont really play in gv's as I dont have the patience, so no help there.  I have a creative sb x-fi sound card set to 5.1.  my headset plugs directly into the sound card (it is not a usb).  and my game setting is set to use whatever windows is set to.
I can clearly hear the planes and which direction they are traveling  when going over/under me.  I am not a sound expert so I dont understand this whole discussion about "not playing properly".  then again I dont really have expensive equipment or are a sound aficionado like some guys here.
I read what skuzzy and challenge are saying, there has been a few threads about it.  I just dont "hear" what they're talking about.  I think this is the confusing part for most of us.  our definition of "play properly" is not the same.
I have used mono sounds that I had saved from a while ago, think they were mitsu's, but to be honest I cant hear the difference between them and let's say tb's sounds.  and I am talking about surround sound, and not the difference in engine sounds, etc.
damn it, I hate you guys, I am gonna drive 40 miles to fry's so I can get a different headset to look into this further  

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semp