Searching for "usb 7.1" on amazon.com gives these top products with decent rating:

http://www.amazon.com/Vantec-External-Channel-Audio-Adapter/...

http://www.amazon.com/Sabrent-USB-SND8-8-Channel-External-Su...

Here's the Razer Tiamat headphones, I'm using them and like a lot:

http://www.amazon.com/Razer-Tiamat-Surround-Gaming-Headset/d...