If you have a USB headset then it will be completely separate and independent from the Realtek audio system.
The Realtek devices will control the various 3.5mm sockets on your motherboard. You will most likely find them on your back panel and may also have them on the case as well:
USB devices on the other hand are distinct audio devices in their own right. They have their own drivers, both software within the operating system and hardware driving the speakers.
I cannot speak for your actual problem but judging by the "USB PnP Sound Device" I would suspect that you have a very generic USB headset and it may be that the hardware is not 100% compliant with how the generic driver is passing data to it.