Following all the steps above I can't get the kext to load.
I didn't have to edit any of the files.
I have SoundMax Digital Audio;
Vendor 8086, Device 266e, ICH6-M (which is already in the AppleAC97AudioIntelICH.kext)
AD1981BL which is ADS74 going by the datasheet (which is already in the AppleAC97CodedAD198x.kext)
No Information appears in System Profiler
When I try to load the kext it says;
~ root# kextload /System/Library/Extensions/AppleAC97Audio.kext/Contents/PlugIns/AppleAC97CodecAD198x.kext
16IOAC97AudioCodec is not compatible with its superclass, 9IOService superclass changed?
kextload: a link/load error occured for kernel extension /System/Library/Extensions/AppleAC97Audio.kext/Contents/PlugIns/AppleAC97CodecAD198x.kext
load failed for extension /System/Library/Extensions/AppleAC97Audio.kext/Contents/PlugIns/AppleAC97CodecAD198x.kext
(run kextload with -t for diagnostic output)