cerspense
New Head-Fier
But it is possible to place virtual sound sources behind the listener even with stereo speakers...
This might be possible with a binaural recording in an ideal environment. The problem with intentionally making things sound like they are coming from behind you is that we mostly sense this from distortion resulting from the shape of our ears. There is a lot of software that is able to do this pretty well with headphones but it is a lot trickier with speakers.