Extra GPU, Not enough 8pins second PSU?

Hardware PSU
1

So I finaly got my Z87-ws back after 5-6 week RMA. And I am getting ready to buy my first GPU of the 4 GPU setup.

The idea is ill have 3 GTX 780's and a single GTX 560 for dedicated Physx. Already own the 560)

Now I was just going to go for a stock 780 but decided to drop the extra on the EVGA Classified. Thats all and good but my PSU, Silverstone Strider Gold Evolution 1200Watt only supports 4 6 pin and 4 8 pin PCIe power jacks. Thats fine and all except the GTX 780's require 2 8 pins each. They each come with 2 2 6pin to single 8 pin converter so that would cover the third GPU but there is still a GTX 560 and a single 6 pin on the motherboard.

Now I was thinking simple 2 molex to single 6 pin but that only provides 2 of the 3 12v signals. Plus I only have 2 more full molex cables I could use. (Using one full cable defeats the purpose right? to many amps for the 12v cable to handle.) 

So im not sure. However I do have a second PSU (Non modular) 700Watts 4 years old from coolermaster that I could build a mount for. It has 2 6+2 pins. That would free up 4 6 pin connectors for everything else im just not sure if using a second PSU in a system is a good idea. The Silverstone has a 100A rating on the 12v rail and the Coolermaster 52A on the 12v rail and I would short the PS-ON signal on the second PSU to allow it to power on.

I have a Phantom 820 so space is not an issue. however one this that is an issue is if I power a single 780 on the second psu, it will be powered on allways if I dont physicly turn off the PSU? Any ideas on how to turn off the PSU automaticly e.g. a switch powered by the first PSU on the PS-ON signal? 

Just could really use home help with this. My electrical engineering is very limited to 3 months building switchboards and Highschool Physics.

Rudster

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just get some adapters 

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I want to see a surround 1440p setup, powered by this rig, Rudster. It would be pretty awesome.

And you don't need the dedicated card for PhysX. Since a single 780 is capable of maxing games with PhysX enabled. Trust me on that.

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why in the world do you wanne go triple SLi setup on a Z87 platform with only 20 pci-e 3.0 lanes? its just a waste of money, if you want to go triple of quad gpu setups then go  Ivy-bridge E with 40+ lanes of pci-e 3.0. i7-4820K with Socket 2011 X79 mobo. with a dual gpu setup you will be absolutly fine with hasswell but for  triple and quad setups, you will be a way better of with ivybridge -E. 3 GTX780´s will get bottlenecked at 4x... Z87 is just not made for it.

i would recommend stick with 2 GTX780´s on hasswell. but thats personal ☺

back to your question, you can get some splitter cables. if im right ☺

Grtz Angel ☺

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On the GTX 700 series and Z87-WS, There is a very minimal bottleneck at 4 GPU's None with 3 way SLI. I have tested against a mates rampage 3960x quad titan build. All I saw was a 3% bottleneck on all 4 GPU's in comparison on the rampage. 

Skullabyss, Just getting some adpaters is stupid. Just for one 6 pin, you need 3 molex cables to supply the ampage requirment for 1 6 pin pcie. Doing so is just asking to burn throught the 12v cables and cause damage to compnants aswell.

Berserker, I do a lot of work in 3d animation and game enviroments, reason why I want that extra 560 is to dedicate all graphics rendering to the GPU's. Though there is a chance I might sell it on to a mate. 1600p surround setup is on the table.