Finally got 5x Cards working on Asus z97-A MB. It had no issues detecting the graphic cards, set at 1x *3  and 8x *2. But installing any driver would crash / BSOD on Win 10. Turns out that Crossfire was the culprit for whatever reason and was getting activated by default. Disabling crossfire if I got the time to do it before it crashes, would make it crash! My config was 2 GC's on MB attached directly and the others using  powered risers . 4 Graphic cards on this set up worked without any issues. Addition of the fifth would crash with a garbled image and reboot every time the driver tries to get it self installed. Tried everything, including cycling graphic cards, installing one at a time and so on. And disabling cross fire everytime I had the opportunity to do so I.E 4 graphic cards and then disable cross fire, and then load the fifth => crash. It wasnt an IRQ or Resource issue, as I disabled every god damn onboard device, xchi, Lan, OGC, Sound... Only active items from Bios were PCIE & SATA controller.

Solution was the last resort I had, which was leave only one GC on the MB and use risers for the remaining 4 GC's. Logic was that since one slot will operate on 8x while the other is operating on 1x, it would never try to crossfire. Based on this hunch I proceeded and well, WTF, shit started working like there were no issues. F*ck! Spent 3 days reading everything, applying every patch and mod, installing ReLive drivers and such. So from my experience it was the 8x *2 or Crossfire that was the culprit. Leaving this note here, so it may help others and not end up eating their mining time figuring this out. This may be another factor that you may want to scratch out when troubleshooting. Hope this helps!