Importantly, the USB Audio Device Class 3.0 continues to support both analog and digital audio. The two secondary bus (SBU) pins are still allowed to be used for non-digital audio transfer, so ...

The new Lattice USB 3.0 Video Bridge Development Kit simplifies integration of USB 3.0 audio and High-Definition (HD) video connectivity for a wide range of applications, leveraging the ...

They are taking digital audio and converting it to analog for the headset. In effect the USB speakers have a built in sound card. Also, I notice you have the RealTek digital output set as default.