The other issue I'm having is the 1x to 16x riser cards don't want to work in the 16x slots. The system won't post.
I have 6 cards running like this with ubuntu using the 1-3 extender off a 16x port, but it did crash after 9 hours it looks like.
I'm running 7 cards today with EthOS. BIOS doesn't post at all. But system boots up and runs.