I think it's our brain that actually does the work with the fake 5.1 headsets, like the sound is altered somehow, so sounds sound slightly different depending on 3D position. Then we subconciously interpret that as the sound coming from the front or back... I mean how can we tell a sounds position with our ears, considering the fairly simple anatomy of an eardrum. The sound must be distorted depending on the shape of the ear (more distorted from the back), then our brains decipher it and can decide where it's coming from. The fake 5.1 is probably mimicking this....but anyway there is a big difference between normal stereo and the 5.1 mode, I'm not exactly sure how but it's easier to place sounds with it.
I am the one who knocks...