Being excited about 5 cards working, I tried connecting the 6th and going to safe mode to install drivers.
All 6 cards are shown in safe mode with no cards needing drivers. Yet booting windows normally fails.
Not even sure what to try now.
What build version of Windows 10? 1607? 1703?
Go to PC Settings:System:About to find this information.
6 works with build 1511.