So, an update: I decided to revert to Yosemite for now. It's disappointing but when previously working HDA.kext patching in Sierra suddenly started to fail during startup I felt I had to draw the line. I did "backport" several of your changes into my Yosemite install though Shilohh, among other things I changed to the MacPro6,1 system definition. I also replaced the old DSDT and replaced it with: SSDT-0 (with your various fixes and tricks) SSDT-1 (Nvidia Drivers gave me a ~10% performance boost over Sierra with Apple drivers, no AGDPfix needed to load) SSDT-4 (for a KT4004 4-port USB 3 card) Plus a generated SSDT-9 for power management. (included a replacement of the X79X86.kexts in S/L/E) Not sure, maybe I can use the SSDT-8 USB-fixes on Yosemite too? I haven't tried it yet. I gained a more compatible system definition, I threw out GenericUSBXHCI (finally) and thereby future-proofed the install some more. All in all maybe one step back and two steps forward. A few things remain; like testing a migration of the custom kexts installed in S/L/E to the EFI-partion, but I am concerned as to what the cause for the audio issues are since my current install used your old HDA-patching method which was based on PikerAlphas-variant, not Toledas (I might misremember that). Perhaps it's more reliable? My fear is that the audio issues will return if I start moving the kexts around and/or change patching method. Oh well, that's in the future. Thanks for the awesome guide and Happy New Year.