My friend just picked up the Tritten ax720's yesterday, and I was really impressed with the sound quality. The 5.1 left a bit to be desired, but it did the job. Those fall in the $150 range.
As for the xp500's, I would say stick with Astro's if planning on dropping that much money on a headset.
Those are just my suggestions though. Never really used them myself. Can only recommend that one I listed above.