I remembered that MacPro7,1 caused some issues and that only my current smbios worked properly. The IOREG is definitely with NRX disabled. (As you said, just one monitor and no hardware acceleration)
i do not know if NOOTRX needs to use ImacPro 1.1 Smbios
For your CPU is more appropriate to use MacPro 7.1 Smbios
i would try to use in this way if possible
Happy you solved initial problem but i think is it possible to improve your system configuration