Have you checked out C-Media Company Information
and downloaded their drivers for Windows 7. They have beta ones for Windows 7.
I think 8738 drivers have generally been backward compatible with older models. I am going to try them out with my SIS onboard audio tonight. I have currently got the CMedia 5.12.01.0051 drivers working fine under Windows 7. I have also used the older SIS 7012 driver, but Windows 7 didn't know how to change the volume levels with this driver.
Windows 7 by default wrongly detects the onboard sound device as a Realtek AC97 adapter.