I'm not quite sure why you'd want true 7.1 in a headset though. I've always been sceptical even with the 5.1 ones (true 5.1, mind you), and cheaper sets are available (like the Roccat Kave set). However, once I used the Kaves, I must say I changed my mind. 5.1 is awesome. But OK, back to the question.
True 5.1 exist (quite a lot of them, actually). Good ones (not extreme, but "budgeted" ones) include the Roccat Kave, Razer Megadolon and Razer Chimaera headsets. 7.1 is hard to master due to the amount of connectors you need and the amount of speakers you'd need to plant into the headset, but I know a lot of the cheaper sets can produce stunningly accurate 7.1 with software from Dobly, like the Logitech G35 and Razer Megadolon headsets. Both are really good, and I'd recommend anyone of these to to anyone.
For you though, I'd recommend the Roccat Kave set. It fits perfectly in that motherboard of yours (one of my friends has the set on an 8-channel mobo), and it truly performs like a beast. Turn it up loud and you simply cannot keep it on your head, you will pop an eardrum (it goes loud enough for you to place it in the desk, turn on some music and still hear it in the next room). Sound quality is great, and you can switch between profiles quickly and easily.