Ultegra FC-R8000 Right Crank Arm Creak
It seems that after all was said and done - putting the new crankset on another bike showed that the creak followed the crankset. Thus, the issue was a poorly bonded/other issue with the right crankarm or power meter.

My stock PF90BB was a bit loose as well, so the Token BB mentioned above was another benefit (and better design IMO).