Well some bad news.
The 4th PCI-E slot on the board appears to have failed during benchmarking on Nicehash (I walked off & it had rebooted when I came back).
Any card plugged into that slot is no longer recognized.
Looks like this will be a 3-card machine!
I'm surprised it did run at all... you expect a bit too much from the sata connectors :-D
You probably burned the riser (witch I did with a rx 470 on my t5500).
My 8 pin to Pcie PEG arrived yesterday, I tested them right away with a R9 290x.... they give enough power for ETH, but dual mining it rebooted after pushing dcri to 28.
Although, I power 2x480 dual mining without problems out of the same connector it's running for >12h now.