Two things we have to remember :
- Do not use "Inject NVidia" to prevent from black out after booting. However, this leads the issue of HDMI audio because it was required for HDMI audio.
- Drop this kext to enable HDMI audio here : http://www.tonymacx86.com/threads/gtx-770-hdmi-audio-how-fix-el-capitan.183955/
No others worked for me, but here goes URLs for your information because it is not sure that "HDMIAudio.kext" triggers on top of others :
Summing up, avoid "Inject NVidia" and drop kext of HDMIAudio.kext, that's all.
ASUS GTX 770 DirectCUII 2GB DDR5
Gigabyte B75M-D3H / 16GB