iMacPro 1,1 Worked like a charm with iGPU disabled. H264 and HEVC hardware acceleration is now enabled. As a bonus to the change, I even received a bit of an uptick in Cinebench which, is always welcome.
Also in the guide was an interesting section on AppleALC. I think I will make those changes as well since it seems to be the wave of the future.
Thank you for taking the time to help.
[EDIT] Out of curiosity, I tried enableing iGPU on this system config. MasterZee still works perfectly with the intel graphics active.