Splitting an 8-pin PCI-E connector to dual 8-pins is not recommended. That's a good way to overload the PSU cable and rail with up to 300W. That PSU has 4 PCI-E ports. With 3 cards and 6-pin risers, you can use 3 PCI-E ports for the VGA 8-pins and use a 8-pin to dual 6-pin splitter cable to power two of the the 6-pin risers. The last riser can be powered with a 4-pin molex to 6-pin adapter cable.