5.1 headset is not needed. You have a sound card with Dolby Headphone, which will create surround sound using just stereo headphones/headset.
Razer Carcharias is a decent headset, recommended by quite a few people. They appear to be open, so will let a certain amount of sound in. I am wondering if it might be better to get an on ear (supra-aural) pair. I use over ear (circumaural) headphones, which are open, but when playing a game, doesn't matter if outside sounds can get in, because it's very hard to hear anyway, as outside noise gets drowned out. The volume would need to be pretty low, as it can be hard to hear your own voice, let alone anyone shouting from the next room etc. As supra-aural are on ear, sound is more likely to be heard while having more volume from the headphones/headset, as the sound can get round the ear cups, and doesn't have to travel through the ear cups, as it would with over ear types.
The downside to using on ear is they are not that good when it comes to surround sound.