Powered risers. Here is an interesting reply from someone on the litecoin mining sub redditt out the board

[–]TehGogglesDoNothing 1 point 10 hours ago
I looked up the manual for your computer. The 16x PCIe, all 3 1x PCIe, and the NIC all share the same bus. The x4 PCIe is on its own bus. You might want to try putting one card in the x4 slot and the other three in x1 slots.