I believe astro's mixamp uses 3.5mm headphone/mic jack and I don't think there are adapters for using a usb headset on a 3.5mm jack.
On a related note I think a similar product was just released recently, so depending on what you want to use it for (pc/console) I'd wait for the reviews on that to come out before you decide since they're selling for the same price.
http
/www.creative.com/soundblaster/tactic3d/recon3d/
Is what I'm talking about.