I am not enaugh familiar with this kind of device injects, that I could give you an suitable advice on how to add it in your case, but I think you should know that you will still need a patched AppleHDA kext even with having correct device inject.

Maybe this VoodooHDA fork is an easier solution suitable for your needs - alltough I could understand if you don't like using it as I have reasons to dislike it myself, like System Profiler crashs, problem after wake-up from sleep, etc...

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