The speaker icon on your desktop will allow you to choose which one you prefer for each device.
The Realtek drivers would provide the best results.
This is not so. You cannot just select which driver you would like to use. The video card has an HDMI port. HDMI carries sound. The Nvidia audio drivers are used for this and nothing else. The Realtek drivers are for the motherboard's onboard audio. Speakers plugged into the audio jacks in the back of the computer use these.