Apologies as this is my first post and a bit of thread necromancy, but if, like me, you've been googling all night for the answer, this might help!
Like others, I have a CMI8738. The reason being is that I have a keyboard connected to my computer connected by old-fashioned midi ports through the old joystick controller. Works perfectly. At least it did until I wiped and Windows 8.1'd.
There is a Windows 7 64bit driver at Softpedia which works perfectly - search for CMedia Oxygen HD CMI8738 Audio Driver 7.12.8.1740 for Vista/Windows 7.
If you try and run this file, it will tell you it's not compatible SO.....
Extract the ".exe" file using winzip, 7-zip etc (it's just an executable zip file). Find the "drivers" folder and hey presto use the "Find compatible driver" from your device manager, point to this folder and it works perfectly.
Now if I'd only found this thread 3 hours ago.......