Dunno about 3D sound on headphone for xbox`s, cos 9/10 times, headphones are just basic sterio. some have mini subs though, and rumble features.
Heres what i`d do.
1) Buy an external sound decoding device, that has headphone outputs on it. Such as a Creative Labs SoundBlaster Extigy.
2) Buy a pair of wireless headphones, with chaging unit/transmitter combo as well, you dont hve to constantly buy batteries then. Makes sure that they are stereo.
3) Connect the Xbox to the decoding unit, and the headphones.
4) You will then get a virtual surround out of the headphones(depending on the decoder).
I get quite realistic sound placement with my wireless headphones, connected to a Audigy card