I was wondering if i could get away with adding a second EVGA GeForce GTX 680 into this system with this power supply still in operation. I have had it for five years now and it has never given me an issue with the previous cards. (Is five years too long to have a power supply in service under this kind of strain?). Also it looks like i will have to use the molex adapters that come with the card when I add a second. I only have one open 6 block rail and no open 8 block rails, but plenty of open 5 blocks.
You're likely going to be decreasing your power consumption, and had much more than neccessary to begin with
As long as it's still stable there should be no reason to swap out the psu
Check the card, it may come with a 6 pin to 8 pin adapter, some do these days
Edit; reread it, missed 680 SLI first time, power consumption will increase, not by alot but I'd upgrade to have the connectors