since nobody else has answered this, I will chime in here...
With standard single video cards with dual monitor capabilty, it never mattered which output connector you used (the vid card would sense which one was plugged in)... I can only assume that it wouldn't matter in your case either. In SLI mode, the 2 cards function as 1 single card.
I can almost assure you that if it did not state in your video card or motherboard manual which connector to plug the monitor into, then it doesn't matter. when you plug it into any "socket" it will be recognized and configured from there. In any case it won't do any harm to plug it into a different output