I think the one you have selected right now is the USB portion of the headset.
It has a built in amp/dac and all that stuff.
So that is the settings that cuts out at lower volumes?
The reason the realtek does not play on the headset is because it is connected to jacks on the case for normal headsets(you may be able to plug the headset directly into the front GREEN jack on your system, but the mic may not work). The also have adapters to allow these 4 connector TRRS sets to be used with the normal green/pink jacks on computer, but this would bypass the amp with its full set of controls.
You should also be able to have the usb and 3.5mm back on the computers green jack(again the TRRS is my only concern as it works with some and not with others.). With that setup you may be able to use the realtek output, but not the digital ones because the 3.5mm jack in this case is analog(second down in your image(front green port) or the top one for the back green plug).