Actaully you have to change something in the BIOS after that it works , wait i will check what i did with my Gigabyte motherboard and tell , can;t exactly remember what i had done.
Yes you're absolutely right. Its Intel HD Audio/AC' 97.
AC' 97 is the compatibility mode (you've to set it in BIOS), most cables/audio headers coming with cabinets are for outdated AC' 97 not the newer Intel HD Audio.
Desktop Boards — Troubleshooting audio issues
Some cabinets come with both:
*www.guru3d.com/imageview.php?image=8605