Using an external mixing board with my usb headphones (for surround sound vs stereo) (Ideas please)

So for starters I have a usb to 3.5mm headphone and mic splitter. I have a zalman clip on mic and a pair of ATH-M50s.

My problem is that I can only get stereo sound through the USB output but I also have an old Turtle Beach PX5 amp that has the headphone jack on the front in full 7.1 surround. If I plug my mic into the usb and my headset into the PX5 then when I chat in parties everyone can hear me but I cant hear them.

Here's what I am thinking. Take the output from the usb and the PX5 amp and mix them into an external 2-Channel mixing board and profit?

I know there is probably an easier way to do this so please help me see the light.

Also my reasoning for this is that having that surround sound in the headphones vs just stereo is kind of a major game changer when it comes to games like Overwatch, Battlefield, Fortnite etc..