Hi guys i just thought i might throw some insight out there for you guys. Maybe your onboard Audio doesn't work or maybe you're looking for better audio heres a PCI Sound card which works from 10.6 straight to 10.11 it sounds beautiful i actually forgot how well it sounds compared to onboard audio. you can pick up Creative Sound Blaster Audigy 2 quite cheap on eBay its a old sound card but still sounds great
You need to install the KX driver which has its own built installer for OS X also...
Creative Sound Blaster Audigy 2 working in 10.11

Creative Sound Blaster Audigy 2 working in 10.11