The difference you're paying for is Digitally Processed 7.1 Dolby Surround Sound, whereass the Bravo is 5.1. As all headsets have a cord from the xbox controller to the headset, the Delta headset just has an adapter (click link to read more about it) which will transmit your voice wirelessly through bluetooth technology for Xbox 360. This is one of the few bluetooth headsets on Xbox 360. This adapter can also be bought seperatly for $30 and is compatible on most of Turtle Beaches latest headsets. They are both wireless though (from your Xbox to your headset).
I own a pair of the PX5s (run for $270), which basically is the same thing, but doesn't come with the adapter for Xbox 360.
If you have the extra money to spend, go for the Delta pair. It's great for playing shooters, guitar games and blu-ray movies! Especially great if you have a blu-ray player on a laptop so you would be able to experience the true audio experience on the go. 
Merry Christmas! Thanks to the both of you for your informative replies! Sorry it's a little late. Sebye - exactly the reason you've mentioned about the disadvantages when going the high end route (the Sennheiser/Astro combo) - I don't want the hassle of the place I purchase them not being local. So I will likely be going the Turtle Beach Delta Limited Edition which I can pick up at my local Future Shop.
matchew - My sisters BF has the Turtle Beach Bravo Limited Edition headset and loves it. I could imagine that going with the next model up (to the Delta) would make a difference in overall playing experience.
A quick question. Seeing as how I have the XBOX Chat Pad attached to my controller, how would the headsets Bluetooth adapter attach to that Chat Pad? Would the two of them be compatible shape wise? Would really hate to buy the Delta headset, only to find out that the two won't fit together due to a difference in construction! 
Regards,
Jason
