My editing note: This Spoiler covers irrelevant content.
Warning: Spoiler! (Click to show)
I have finally discovered something I should really have been looking for in the first place, which is summed up in this shot of the AIS3_GPUBoost screen:
In other words, there is as yet no software support for the iGPU at all, neither in Catalyst from AMD nor from the BIOS or AIS3 from Asus. You can see it in this CPU-Z screenshot:
As for Firestrike &etc. I need to hold off any further installations until I have full hardware support.
But here's HWMonitor in action.