The chipset is listed as "AC - 97 Audio, ADI1981HD via ESB2 / high definition" in the Xref. The complete document is available at the link below. From what I can find on the Intel support site, you are correct and it does not appear that there is a driver for this chip set. Maybe you will have better luck than I had.
Xref - Page 95 contains the 9228
This audio chipset is used in a lot of Boards. I know it's in HP, IBM, and Dell ( http://en.community.dell.com/forums/p/19268952/19601455.aspx#19601455 )
boards. I bet it's in a number of Intel branded boards as well. I also goes by the name SoundMax HD.
Very frustrating issue.