It should also be noted that when connecting more than 3 GPUs on a MB, you need "powered" risers, soerboard. that your GPUs grab their BUS power from the PSU instead of from the moth. Otherwise you could end up frying your MB or GPU.
the gpu cards plug into one end of the riser. then other end of riser goes into mobo. then the extra power supply cables connect to the end of the riser attached to the video card? this way the power goes from psu to gpu instead of threw board?