Question MSI mpg x570 will not POST with known working gtx1070, gtx1080, POSTS and runs with old gtx560

[JonnyHeat]

Recently picked up a MSI mpg x570 Gaming Wifi board, and the system will not POST with either my EVGA gtx1070 SC, or my friend's MSI AERO gtx1080 (both run just fine in his rig, and well as in my old p55a Gigabyte board.) It runs fine with my old EVGA gtx560 ti. I've tried everything I can think to do - clearing CMOS, flashing the BIOS to different versions, drawing a pentagram around it and sacrificing a chicken, etc.

Hardware is as follows:
MSI mpg x570 Gaming Wifi motherboard
ryzen 5 3600 running stock (tests fine under 4G burn test)
16G corsair vengeance rgb pro 3200 (tests fine under memtest)
CoolerMaster GX 750w PSU

EVGA gtx560 ti (runs just fine)
EVGA gtx1070 SC (will not POST)
MSI AERO gtx1080 (will not POST)

I had MSI support on the phone earlier, and they said "hmmm that's weird," and sent me a beta BIOS revision which I flashed to the mobo yet alas, did not help. The tech claims they're going to try to clone my build there and replicate the problem. I'm absolutely boggled at this point. Any ideas?
Thanks in advance.

 

[vapour]

have you tried the second PCIEx16 slot?

 

[JonnyHeat]

yes... 560 works in both, the two 10 series work in neither and prevent the system from posting

 

[dorsai]

Reset the BIOS to defaults...it sounds like the PCI-e link speed has been changed from Auto.

 

[JonnyHeat]

PCI_E1 link speed is set to auto. I've also tried manually setting it to gen3.