Gaming headset that others can't hear?

I'm sorry to post another headset topic, but wading through 4500 responses for this specific answer seemed a daunting task!

I want to get a gaming headset for the Xbox 360 so that I can play Modern Warfare 2 without bothering my girlfriend with explosions in the living room.

I bought the Turtle Beach X41 and they sounded nice, but she could hear everything that was going on while sitting next to me on the couch (down to the dialogue of the incoming chat), and I could hear her watching youtube videos on her laptop while I was gaming.

I want the game sounds to stay in my ears, and the youtube sounds to stay out.

I'm willing to spend up to the $250 - $300 mark.

Most reviews I've read don't mention anything about whether other people can hear you gaming!

Options I'm considering:

Turtle Beach HPX with A40 mixamp
Sennheiser PC 350 with A40 mixamp
Tritton Ax Pro

I've read that the Sennheiser and Tritton both keep sound out, but not whether they keep it in. I haven't read anything about the TB HPX keeping sound in or out, just that it's a great gaming set.

Can anyone who uses any of these set ups advise me on whether they keep the sound in/out the way I'm describing here?

If you have another suggestion in the $250-$300 price range, I'd love to hear it.

Thank you for your time!

You know, I tried the TB X41, and after posting this thread I tried the Tritton Ax Pros and returned them too. They were ridiculously uncomfortable! I read a review that said it felt like you were wearing a bear trap hat, and I couldn't agree more.

I bought the X1 model on a whim since it was the only one Best Buy had in stock that I hadn't tried. I wasn't expecting much out of it, but it really is a good headset. It's not surround sound, it's not amazing.. but it does the job, and it keeps the sound in wonderfully, as you mentioned!

I am really impressed with the quality of this relatively cheap product.

I still intend to go the mixamp route with a more quality set in the near future, but for the price, I'm keeping these X1's and using them until I feel confident in which higher quality set to go for.