(In reply to Matthew Fox from comment #30)
> Just to confirm, the freezes and hard lockups still occur and the
> corresponding messages in dmesg which I also attached.

Weird; the xrandr output and Xorg log file show that the workaround is working
as intended, Xorg is no longer using the dGPU; not sure why it's still getting
powered on.

I'm not sure about the sound messages, but I'd guess they're a symptom of the
dGPU powering on, not its cause. You could try if radeon.audio=0 on the kernel
command line makes any difference though, just in case.