All the 570's I've seen have 2 - 6pin plugs. This is a higher power version.
I would not use the molex because that card uses A LOT of power. Like GTX580 power.
You need to contact Asus because I cannot find any info on using just 2-6pin.
Some cards you can use 2-6pin instead of 1-6pin and 1-8pin, but I doubt it on such a high powered card.