I've said it before and I'll say it again, you have not played "Thief" if you haven't played with an Aureal card. Utilizing NASA simulator technology, the Aureal cards could make positional sounds whose position you could determine laterally and vertically with just a stereo pair of headphones.
(wear headphones for this one)
Unfortunately things ended very badly for Aureal. Creative brought them up in a frivolous patent lawsuit. Aureal eventually won, but the legal costs involved in the suit burned up their money and they were forced to sell out to Creative, who shitcanned the A3D tech to mainstream their inferior EAX soundcards.