Backshark V2 not recording audio in Shadowplay

I've bought the Blackshark V2 + USB sound card and I cannot record the game audio using Nvidia Shadowplay.

I was able to find that if I select the Razer USB Sound Card as the output, the shadowplay record works as expected, meaning that the game sound + the mic output are being recorded.

But, if I select THX Spatial Audio, the record only contains my mic output.

I'd really appreciate any help.

Thanks