Since the adapter provided the surround, there should be a couple of options - using on-board Realtek v-surround or if you are using win10 enabling "sonic" spatial sound enhancement.
For Realtek right-click on the speaker icon and select "sound manager", select "speakers" tab, and make sure "speaker configuration" is set to "stereo" and "headphone virtualization" is checked / enabled. Example here.
To enable Sonic, right-click the windows speaker icon, select "spatial sound" and select "windows sonic for headphones". Example here, has to be creators update version 1703 or later.
Don't use both at the same time, just one or the other.