5.1 audio

Hi, I Just installed osx high sierra 10.13.1 on my system. Installed NVIDIA WEB Driver for my GTX650 card also. Display out is going through DVI cable and Connected SONY IV300 5.1 audio system via HDMI port from the Graphics card. But I can't activate sound .. Please help

My Build; Motherboard – ASUS Rampage 2 GENE Processor – Intel i7 920 @ 3.21 RAM – 12GB DDR3 Corsair Graphics – XFX ATI Radeon HD4890 HDD – 256GB(SSD), 1TB, 1TB, 500GB, 120GB Optical – LG Blu-ray Writer Sound – Onboard 8 channel (I have 5.1 surround working) Network – Ralink R2870 with...