Still stuck. I've tried the following, in this order:
- Updated BIOS to latest (3402, was previously on 3301) & then use Optimized Defaults w/changes as suggested by you
- disable Bluetooth, WIFI, and Ethernet controllers
- remove all external peripherals
- remove all PCI-E devices except GPU
- disable USB3 (Asmedia) controller
Every time I get a reboot after PCI Configuration Begin. If you build a Sierra boot USB as you've described, are you able to boot from it? Asking in case you wrote by memory and perhaps missed something? I'm not sure what else to try! As I mentioned as well, with 10.10 I need AppleACPIPlatform.kext and IOPCIFamily.kext rollback kexts to avoid a reboot at this point, but I haven't read anywhere about Sierra needing these.
Thanks for any further help...