I read that most headphone enthusiasts (some over at head-fi) seem to agree that 'surround sound' or 5.1 headphones are a marketing idea that simply doesn't work well. While there are some models with 4 or 5 drivers on each side, they simply don't beat a quality pair of stereo cans. My experience is limited, but I do have a pair of each type, and have tried different sound settings through my Creative X-fi software, and I agree.
I tested with sound effects and positional cues in PC gaming software.