Thing is that HDMI sound might not work if you are using Legacy Mode for boot in BIOS.

Basically you need to do the following (Less than 5 minutes): 

1. Run cmd.exe as administrator

2. Go to C:/windows/system32

3. Run mbr2gpt.exe /validate

3.1 If you encounter en error that it can only be used from the Windows Preinstallation Environment you will need to use the override command

3.2 run mbr2gpt.exe /convert /allowFullOS if 3.1 applies, else just run mbr2gpt.exe /convert

4. After succesfull step 3.2 restart laptop and enter BIOS (FN + F2)

5. Go and modify the BOOT Mode from Legacy to UEFI

6. There you go, HDMI sound is on and your TV will appear in the sound playback list when you connect it.