Pretty detailed report. The quoted text seems like the key point. It suggests the problem was triggerred by the
installation of the 2 new GPUs. It could mean it's the number of GPUs or a specific GPU. Try removing
one or the other new GPUs to try to stabilize the system. You could also try swapping risers and slots.
There should be a pattern that leads you to the cause.
I have done so, I moved them around switched to different slots. I am able to use the older one with either one of the new cards without it crashing;. And only once did it crash with JUST the two new ones.