Hi Elucias,
They are different audio software devices.
The RealTek driver comes bundled with many soundcards or other equipment. I had problems with the Realtek driver using hi-res files under Windows 8.1. They were resolved by uninstalling the RealTek Audio device driver and allowing Windows to restart and automatically install the Windows HD Audio device driver. If you experience similar issues then you might try that fix, but the RealTek drivers may have been fixed since I had to do that.
The JRIver ASIO (Audio Stream Input Output) driver bypasses all other software devices and talks directly to the hardware. It should yield better SQ than the Realtek device.