sometimes you have to have the same bios on both cards to run sli. I've read it on toms several times.
If they're two of the exact same card, sure. Considering they are not the same cards, though, I really wouldn't even try it.
Bios for the PNY card (going off of OP):http://www.techpowerup.com/vgabios/125731/pny-gtx660ti-2048-120723.html
Bios for the EVGA card (again going off of OP):http://www.techpowerup.com/vgabios/127140/evga-gtx660ti-3072-120806.html
They are different files, and have different settings, so while it may
work, that's a big chance to take, and it likely isn't the problem anyways.