Well if you can't use your good sound system to play the game, then I would suggest getting the X11's. The thing is once you get the headset on you won't be able to hear anything else.
I bought the X11's a week or so ago, because I have a small apartment now, and when my kids (they are pretty young) come over, I can still game on with the volume up with the X11's after they go to sleep.
I didn't do much reading up on them before I bought them, but now that I've had them for a few days, I'm really glad I bought them. They really give a full, crystal clear, detailed sound of my games when I'm playing them. I can definitely pick up all kinds of different little sounds that weren't audible even when my TV volume is cranked. I don't have a surround sound system for the TV, so the X11's a perfect...at least for what I need them for. I had to get the additional HDMI connector for $19.99, so I'd be able to run HDMI and have digital optical audio. For $150, I think it sounds amazing, and is totally worth it.