Right now this motherboard is handling GTX 1060 and GTX 1070 cards. I wanted to use risers to increase the number of cards and also I wanted to keep them ventilated. Due to space constraint this 1 to 4 PCIE riser seems best fit for me since it just uses one USB Cable to connect to 4 GPUs.
The safest route is to buy 2 or 3 regular risers to use all of your board's PCI-e slots.
That's a total of three GPUs.
If you want more than that, you're going to need to replace your mother board.