If you're running out of PCIe cables for your GPUs it's a good indicator that you need more PSUs.

If you know that your single PSU is strong enough for the number of cards you are using, you can run the 6+2 to 6+2 connectors directly from the PSU.

The standard 6 pin connector can be hooked up through the 12/24V peripheral chain cable. I wouldn't put more than 2 or 3 on a single PERIF socket.

If you're running 6 cards on a single rig and you have a high-end PSU, you should have 6x 6+2 outlets and at least 2 PERIF outlets for the second adapter chain.