So if you're already asking such questions, I think the smallest problem is whether 6 GPUs run with it... To your actual question: Yes, 6 GPUs run with it.

The GPUs need to fit the PCIe slots, but the board only has one 16 PCIe slot and as far as I know almost all new GPUs need a 16 PCIe slot so....No you can't run 6 GPUs with it.