I had even tried to set the default audio device under Playback Devices, but only the Speakers and Digital Audio (S/PDIF) are selectable and none of options was able to output sound coming from the TV
I experienced this problem 2.
To fix it i did:
Download the latest driver (not from ASUS website). I used Driver Pack Solution for that it has a new driver.
If you got the latest update installed you may need to set your TV as default playback device.
If there's no sound coming out click right under on the sound Picture---> MIXER--> Enable all applications to have sound and turn your sound higher.
And like the other guys said it's important to have the latest NVIDIA update.
ACER PREDATOR G9-791 |Intel Core i7-6700HQ |16 GB RAM |GTX970M 3GB |FULL HD | 750GB SSD | Samsung 850 PRO & 2X M.2 SSD RAID 0
G75VW |Intel Core I7-3610QM |24GB RAM |GTX670M 3 GB |FULL HD | 526GB SSD | Samsung 840 EVO & 850 PRO
GL552VW |Intel Core i7-6700HQ |12 GB RAM |GTX960M 3GB |FULL HD | 256GB SSD | Samsung