HarryD
I have a X99 Classified. I also have 3 GTX980's and a Corsair AX1200i.
I was able to have supplemental PCI-e power and both EPS 8-pins plugged in because one of the GTX980's had a Y-connector for power (I can add a picture if you're not sure what I mean).
 
I'm making custom cables. The Corsair AX1200i has 8 PCI-e/CPU connectors. If I use them all (6 for my video cards and 2 for CPU power), that leaves me with nothing to use for supplemental PCI-e power. Can I use a peripheral/SATA connector for this? Are all the connectors on the motherboard needed for my setup? I'm running 3-way SLI and I do overclock. 

Im not entirely sure I understand your question but from what you've said I can tell you this... you don't have to use the EPS 8 pins's on your mobo but most will use one if they are going to overclock the cpu pretty heavily often, two would be for ln2 etc... Some boards will also have a 6pin pci-e plug connector on the mobo also to supplement the pci-e slots instead of using a extra part like EVGA's power boost. The EPS 8 pin and a pci-e 8 pin are not switchable, they are keyed to there respective connectors specifically, but if you do push really hard you can get the plastic to stretch enough to plug them in. If you do you will fry something so don't. So you should be just using all your pci-e 6 pins for your cards and one eps 8 pin for your cpu. You should be fine with that setup but if your mobo has the pci-e 6 pin plug on the mobo by the pci-e slots, then you can hook one of those up too to give extra power to the pci-e slots but you may not need it unless your really pushing those cards all the time. Hope that helps some. :)                                         

Its true, but it depends on the mobo, cards, the overclocking, if any, etc... but in your setup I would do it since it is three cards and I wouldn't want to have to monitor the system so closely to make sure im not going to have a issue. You could probably get away with out it, but why chance it?!?

Looking at the pinout for the AX1200i, it has 6 peripheral/SATA. One will be used for my Corsair AIO cooler pump, two will be used for my HDD's, with the three I have left over I can power the supplemental 6-pin. I need three 12v and 3 grounds for that.

That LD case is awesome, all alum h20 builders dream. Sounds like it will be one great build when your done. May the mod gods bless your tech!!

With 3 EVGA GTX980's Use Both.
My 6-Pin Pulls 120-130 Watts with my 4 GTX 980 HC Cards.
The 6-Pin will relive the 24-Pin Power Draw and using 3 or 4 Graphics Cards I would say is a Must to use.

HarryD

bcavnaugh
With 3 EVGA GTX980's Use Both.
My 6-Pin Pulls 120-130 Watts with my 4 GTX 980 HC Cards.
The 6-Pin will relive the 24-Pin Power Draw and using 3 or 4 Graphics Cards I would say is a Must to use.

and I also need both 8-pin CPU's, correct?

No, if you are never going overclocking on your CPU and Memory but your PSU has 2 8-Pin EPS Cables then Yes.
It is up to you but this a Classified Motherboard A Power House of a Motherboard.

That second CPU 8 pin plug is for EXTREME (as in LN2) overclocking. There's a very slim chance it will help you any if you aren't cooling the you know what out of the CPU.

The extra 6 pin PCIE supplemental power is for multi video card rigs. Or in my case, a single GPU and a single discrete RAID card (long story, but I always plug it in now as my X79 Dark stopped booting without it using the same cards that were in my X99 Classified).

HarryD
I have a X99 Classified. I also have 3 GTX980's and a Corsair AX1200i.
I was able to have supplemental PCI-e power and both EPS 8-pins plugged in because one of the GTX980's had a Y-connector for power (I can add a picture if you're not sure what I mean).
 
I'm making custom cables. The Corsair AX1200i has 8 PCI-e/CPU connectors. If I use them all (6 for my video cards and 2 for CPU power), that leaves me with nothing to use for supplemental PCI-e power. Can I use a peripheral/SATA connector for this? Are all the connectors on the motherboard needed for my setup? I'm running 3-way SLI and I do overclock. 

Hello,
 
Seeing as your PERF cable outputs should offer 12v I dont see why you couldn't use it for the additional ATX 6pin.

GTXJackBauer
Harry, here, here.
 
1.  I don't know what experience you have with wiring, but I would honestly advise on purchasing a sleeved kit.  I've seen too many stories of folks by mistake, frying the whole system because they crossed the wrong wire with another.
 
2.  You ONLY need 6 of those PCIe connectors for the GPUs and 1 for the CPU, leaving you with one for the PCIe header which supplements power to the lanes.  It is needed when you have mutli-GPUs whether you have a OC or not.  
 
3.  As posted, you're not going LN2 off the wall.  Both of them CPU headers supply the CPU 600w of ridiculousness and that's not what you're doing here.

1. I have a lot of experience with wiring (automotive). My last three systems were built with custom cables I made myself. I have a Fluke multimeter if I need to test voltages.
 
2. I had the CPU overclocked to 4.2 GHz. So I was thinking I need both 8-pins. I don't want to install everything and have to do it again because I need to add another plug.
 
3. Is one 8-pin sufficient for the overclock I had? I also don't want to have blue screens and other weird issues because lack of power. 

HarryD

GTXJackBauer
Harry, here, here.
 
1.  I don't know what experience you have with wiring, but I would honestly advise on purchasing a sleeved kit.  I've seen too many stories of folks by mistake, frying the whole system because they crossed the wrong wire with another.
 
2.  You ONLY need 6 of those PCIe connectors for the GPUs and 1 for the CPU, leaving you with one for the PCIe header which supplements power to the lanes.  It is needed when you have mutli-GPUs whether you have a OC or not.  
 
3.  As posted, you're not going LN2 off the wall.  Both of them CPU headers supply the CPU 600w of ridiculousness and that's not what you're doing here.

1. I have a lot of experience with wiring (automotive). My last three systems were built with custom cables I made myself. I have a Fluke multimeter if I need to test voltages.
 
2. I had the CPU overclocked to 4.2 GHz. So I was thinking I need both 8-pins. I don't want to install everything and have to do it again because I need to add another plug.
 
3. Is one 8-pin sufficient for the overclock I had? I also don't want to have blue screens and other weird issues because lack of power. 

1. Fair enough.
 
2. and 3. You only need one CPU 8-pin for OC's all the way to around 5+/-.  I use one on a 4.4 Ghz OC.  I've seen other daily drivers anywhere from 4.2-4.6 Ghz, of course dependent on the CPU.  2nd pin would only need to be used if you're going say 6/7+, or as we call extreme OCs which shouldn't be run as daily drivers.

The one on the Left (1) above the CPU facing the MB.
The one on the Right is (2)
http://www.evga.com/products/pdf/151-HE-E999.pdf Page 2 ATX_PWR_8P1
But maybe an EVGA Tech will Chime in and tell us.

HarryD

RainStryke
According to the X99 data sheet, the second 8 pin is optional to add stability to your overclock.
(On page 7/21)
http://www.evga.com/support/manuals/files/151-HE-E999_Part2.pdf
 
Unless you are pushing a overclock that has the voltage sky high, I wouldn't even worry about it. Voltages this high require phase cooling if you want to maintain your overclock for gaming.
 

Which one is the Primary and which is the Secondary?
On the board I have ATX_PWR_8P and ATX_PWR_8P1 (I'm thinking 1 is the secondary).

 
The 8P1 is the main, but it shouldn't mater since they both hook up to the same power.

Marcel85cu
i tried to connect the second one but my corsair  750i doesnt have the second connector so its only on ATX_pwr_8p

It has both, upper right corner of your PSU. ATX_PWR_8P1 is the Primary.

CP-9020031-NA this is my PS unit.

yes