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The solution to this problem is to find BootCamp 2.2 in the Apple website and extract the audio drivers from the installation file using 7ZIP. If you’re like me and have encountered this problem, then you’re in luck — I’ve extracted the files using 7ZIP (Note: I only have the 32bit audio drivers for Windows 7, not the 64bit ones.).
If you need the file (note: this is for 32bit Windows), access it through my Dropbox.
Good luck!