Razer devices a pretty powerful when it comes to hardware performance/gaming. They are also well known for providing complex drivers
for their products.
My guess is that when you'll install the headset, the driver
software will provide you some advanced options to choose from.
Among those, there should be some setting to enable the 7.1 sound experience, by overriding your standard sound card settings, and applying its own.
I cannot however guarantee this as a 100% go, it's just a thought to help you decide what to do next.