I have a few rigs with Asrock H81 Pro BTC motherboards all with 6 GPUs each - and they work fine. But in the UK, no-where sells the H81 anymore (they have been discontinued) - so I tried an Asrock Z97 Anniversary and found that it only has 4 PCIE slots and 2 PCI - and I can only get 4 GPUs working with powered risers..
I've also read the H97 Anniversary should be okay, but can't find anywhere selling that in the UK either.
So can anyone recommend a good motherboard to support 6x GPU - and that can be bought in the UK (or Europe)??