System crash going from 2 GPU to 3 GPU, willing to pay for help :-)

I know similar questions have been asked, but after hours of searching I don't see where people have had success figuring this out.

My Setup:

ethOS on USB, but also Ubuntu w/ Claymore on SSD

MSI RX 480 8GB
Saphire RX 580 4GB
Gigabyte RX 580 8GB

ASRock 970M Pro3 Motherboard
1200 Watt PSU
3 risers

Running any 2 GPU together works completely fine, no matter where I put them (risers, no risers, etc). When I add a 3rd GPU, in both ethOS and Ubuntu the miner will start and 1) for Ubuntu/Claymore, it crashes after DAG config, 2) for ethOS it crashes roughly around when the 3rd GPU starts to mine. I'm not sure how to confirm this, because the last log file in ethOS is blank when I go back after a reboot. But thats where showminer ends when it crashes.

My config file in ethOS doesnt have anything in it by default, but I've tried per GPU settings (vlt, pwr, cor, mem, sel, etc), tried disabling globaldesktop, and a few other commands with no luck. Also updated motherboard BIOS for good measure.

What am I missing about this setup that makes it crash? I should have sufficient power, nothing suggests that the risers are bad or connections are bad, it does at least start to mine for about 5 seconds with ethOS, but I'm at a lose on what else to try.

As mentioned, I'd be willing to paypal or point my rig at your wallet for any help to get this thing stable.

Thanks