Even in my Samsung TabPro S laptop, I don't understand how I can get audio simultaneously through both the USBC and 3.5mm jacks. As soon as you plug in the USBC, the 3.5mm sound is cut off. In the same way I am having the same problem. Are not understanding what is the problem? If you find a solution to this please share me as well. I also want to know if its sound card has anything to do with it.
There is no solution. Essentially, the sound card will not allow two people each with a headset (one on USBC and the other on 3.5mm) to hear audio, except taking off headsets and listening to laptop speakers.