For Kepler-based NVIDIA (GTX 6xx, 7xx) in High Sierra, HDMI fixes are rare but needed sometimes.
If you have video but no sound through the HDMI cable, the issue is usually a missing "hda-gfx" property or an incorrect layout ID. WhateverGreen : Ensure you have the WhateverGreen kext installed. These often automate HDMI audio. Inject "hda-gfx" DeviceProperties , add the property with the value hackintosh hdmi fix
This is the most complex fix. Intel iGPUs are notorious for having the wrong and port index mapped. For Kepler-based NVIDIA (GTX 6xx, 7xx) in High