To address just one of the issues you encountered: Mac hardware requires cooperation from its EFI firmware to identify the HD Audio controller to the operating system; Without that cooperation, the OS will not use a present HD Audio controller. Our virtual firmware knows how to identify our virtualized HD Audio controller so that the OS can use it, however we had not anticipated PCI passthrough HD audio controllers, so the OS won't be told to use a passed-through audio controller when running in a VM.
Cheers,
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Darius