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Speedlink Medusa are the only proper 5.1 phones that I know of. I have an older model (non usb version) that I bought about 6 or 7 years ago for playing shoot em ups on my pc. There are 4 speakers in each headphone (front centre rear and sub) and the surround effect is amazing, especially when you consider this is all coming out of a pair of headphones. They have been reviewed very highly by many pc and tech magazines over the years, WHF havn't reviwed them though as far as I know. Available in many online shops here in the UK for around £50 - £60.
I also use them for watching movies when it is to late to use my proper system. I watched the Hurt Locker a few weeks ago on my pc and the explosions have real depth and power to them, you can also hear bullets for example that seem to fly just past your ears. The phones are really comfy as well and you can wear them for hours at a time, eventually they do make your ears warm but this is after several hours.
The phones come with an assortment of cables so you can plug them into dvd players and consoles etc, and you also get a nice bag to store the phones when they are not in use. Oh and they have a 3.8 metre cable as well. The sound quality is good although proper hifi headphones like my Grado SR80is are better for music playback, as you would expect for a proper pair of hifi headphones.
They don't leak that much sound either, well compared to my grados anyway. They do have a mic on them which I don't think you can remove, some of the older models had a removable mic. For the money they are fantastic for both movies and games. Found a
better picture here, look at the "other views".