Can the Xbox 360 do Bluetooth? I don't think it can. I have rarely used the bluetooth features, but I am pretty sure that it can only respond to one input at a time. As in, if I'm playing a game and hearing the audio but then I answer my phone, the audio and chat switch to my phone.
You might be able to do one input using stereo analog and one input using optical audio so that both function at the same time, but I've never tried it. If your reason is that you don't want to switch the optical input every time you switch systems (which I completely understand), I would assume that would work. But if your reason is that you want both playing audio at the same time, I think the headphones wouldn't let that happen.
Hopefully this limited knowledge helps. I really like the PX5s so far myself. If you have more questions or need better answers, you might want to try the Gaming Headphones thread.
Xbox Gamertag: Autowobble