I bought a bunch of those Add2Psu adapters after having issues with getting a psu to power multiple cards. They work like a charm, so I bought a bunch more.
I used them to run titan 780 ti and now about to try 780 ti KPEs in such an arrangement.
Here's a link to my Kijiji ad with a pic of 2 psus hooked up to 4 780 tis. http://hamilton.kijiji.ca/c-buy-and-sell-computer-accessories-system-components-Add2Psu-adapters-Intel-SSDs-Kraken-X60-W0QQAdIdZ570537233
http://www.3dmark.com/3dm11/7817410 A score to show the results