My brother and I both got them yesterday. We also both have Turtle Beach XP400s as well as X12s.
First we tried the XP400s, (wireless/optical connection) and voice quality on both ends was horrendous. Very distorted sounding, sort of like someone screaming into a microphone, as well as audio cutting out.
We tried the same thing with X12s (wired/stereo connection) and got the same results in party chat. Distortion, etc.
Then we tested both exact same setups using the Skype app. Perfect, crystal clear audio. Unlike anything I've ever heard on console gaming.
I've heard of the same issue from other people with different headsets including other brands, even the official Xbox Stereo headset.
Is this some kind of software issue? Any ideas?