Got exactly the same problem. Upgraded from HD 5770 to RX 480 and installed the latest drivers. Now have no sound to the TV. The TV shows up as an AMD HD audio device and it is "Ready" but it has no volume bar next to it and in properties it shows it supports zero channels. The configure button does not work either.
I uninstalled the old drivers before installing the new card and I have since uninstalled/reinstalled the drivers using the AMD clean install option but it makes no differance. I have tried a new cable even though the old one worked fine with the old card and I have tried both HDMI ports on the TV and card but I get the same result. My Ben Q monitor works fine with audio but it only has a headphone socket for output not speakers. I am running W10 64 bit.
Still no reply from AMD?
If you set the audio driver to "HDMI Audio" from Microsoft, it works properly.
I mean, C'mon AMD, when someone who doesn't even make GPUs can write a better driver for your own hardware than you can...
Not only that, but I see you guys are also ignoring the developer threads regarding the awful OpenGL performance from your cards, to the point where NVIDIA cards that are several generations old are faster than your newest ones if using OpenGL!
I bought my first AMD card since the days of ATI, if you can't fix basic faults or even communicate about them, why would I not just buy an NVIDIA card next time?