Since I don't use either of my two optical drives enough to justify their taking up space/power, and I ready have an Apple external USB DVD drive for to MacBook Airs, what about using the two 6 pin cables (already using for GTX 670 to be replaced with Titan) via a dual 6 to 8 adapter for 150W (plus 75 from the slot, now having 225W) and using the two SATA 15 pins via a dual 15 to PCI-E 6 pin for the remaining 25 to 50W needed to cover the spec'd 250W plus another 25 or so to cover temporary spikes over rated power of the Titan? ... .
Since the Titan (like other powerful GPUs) has an eight and a six-pin power inputs, your last concern/question to me, "One thing concerns me though. There are not very many single 15 SATA to 6 pin connectors and there are more double 15's to 6 six pins for sale. Is one enough?" got me to thinking where is the Titan card expecting to receive what level of supply of power. That is, what is it expecting to receive at its six-pin and at its eight pin connectors? I still believe firmly that it is expecting to receive more power through that eight pin connector. But what about the 6-pin connector on the Titan? As a consequence, to re-create a power distribution the way the board is more likely designed to receive it, I'd recommend that the 6-pin input on the Titan be feed from one of the 6-pin connectors on the Mac Pro motherboard and that the 8-pin input from the Titan be feed from the other 6-pin connector on the Mac Pro motherboard
plus whatever power is able to be drawn from the SATA power cable, whether you connect to one or both of those serially attached power outputs on that SATA power cable. Since there's just one SATA power cable (and the power output connectors are placed there serially) that
supplies power from the same one point, I don't believe that the number of ladles (taps) that you place into that power stream increases what the stream can provide as a maximum - you just might exhaust it sooner and there might be another reason not to exhaust it quickly by using
two SATA 15 pins via a
dual 15 to PCI-E 6-pin and that reason is that the wire gauge may be insufficient [ see discussion of 6 Pin PCI Express (PCIe) Power Cable Connector here: [
http://www.moddiy.com/pages/(Reference)-Power-Supply-Connectors-&-Pinouts.html ]. We don't know what the upper limit of that power stream is. But I do have a good idea of what the base amount is and that it's capable of at least getting up to 250 Watts [75w (PCI-e slot) + 75w apiece from each of 2 motherboard PCI-e connectors) = 225w; 250w - 225w = 25w; I firmly believe that the SATA connector can easily supply 25w safely from my prior experience placing up to 4 hards there, especially if you don't have any DVD/CD drives there also
*/]. Regardless whether you connect one or two SATA power 15 pins via a dual or single 15 to PCI-E 6-pin to supply the remaining power needed to cover the spec'd 250W, I'd recommend you combine the known output of one of the 6-pin Mac Pro motherboard connectors (75 Watts) with whatever total amount of power there is to be delivered from the SATA power cable, to deliver the greater level of power that the 8-pin connector on the Titan was designed to receive and use the other PCI-e motherboard feed to give that 6-pin connector on the Titan the power it's probably expecting.
Your suggestion, which was also my first (but now discarded) recommendation, was conceived to insure that the eight-pin connector gets the power it needs, but the amount of power going to the 6-pin connector on the Titan may or may not be enough because we don't know what the top end draw that serially designed SATA power connector is able to safely supply and I have doubts that it's 75 Watts. We may be splitting hairs, but that's where I now come down on the load distribution.
*/]Update - I just located the two Apple DVD drives that came in my 2009 Mac Pro and both are 12v 1.1 amp rated. Watts = volts x amps; so 12 x 1.1 = 13.2 and for 2 DVD drives that would be 26.4. So, we know that Apple considers the SATA power cable source to be capable of definitely supply at least 26.4 watts and with my having powered (by splitters) from there four hard drives rated at 10w each over a long period of time, we know that number is, at least 40. So we are definitely at 250w, especially if there is nothing else connected to that SATA power cable.
BTW1 - An 8-Pin PCI Express (PCIe) Power Cable Connector has (a) 5 grounds and (b) three +12 volt connectors. A regular 6 Pin PCI Express (PCIe) Power Cable Connector has (a) three grounds and (b) three +12 volt connectors [
http://www.moddiy.com/pages/(Reference)-Power-Supply-Connectors-&-Pinouts.html ]; but also see [
http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-12.html ] indicating that two of the eight pins and one of the six pins may really be sensors that allow a card to detect whether an eight-pin connector, a six-pin connector, or no connector is attached. On that dual 6-pin to 8-pin Y cable supplied by EVGA, there's a 6-pin connector that has only 5 pins in it and there's a 6-pin connector with all 6 pin slots populated. On that dual 6-pin to 8-pin connector that EVGA supplies, I recommend that you place one feed from the Mac Pro motherboard into the 6 pin PCI-e connector that has all 6 pins in it and place the PCI-e feed from the SATA power cable into the 6-pin PCI-e connector on the EVGA supplied cable, that has only 5 pins in it.
BTW2 - The following 8 Pin PCI Express (PCIe) Power Cable Connector pic and explanation thereunder may support why Prince134's hack may work for some assuming that the power needed by the video card is otherwise present: [
http://www.moddiy.com/pages/(Reference)-Power-Supply-Connectors-&-Pinouts.html ].
