I have more than one PCIe cable, yes. I am confused, because of a diagram in the PSUs manual. See the attached images. It tells me to use one cable, which would require the use of an 6 to 8 adaptor.
However, I have no personal issues with using two PCIe cables. It just isn't covered and some threads I found online confused the hell out of me, with contradicting statements.
If I do, I assume I should plug the cables in PCIe 1 and 2, as opposed to any other combination. Correct? That's another source of confusion.
BUT: Asus states that the card draws "above 300W" which obviously is more than one rail can provide at 12V 25A.
Treat it as if it’s 2 GPU’s. Do either of the bottom two. The bottom pic shows 2 GPU’s can be plugged into that middle plug, so plug both 8 pins into that. This diagram is confusing AF I agree, but it’s a simple deal, and your thought process is correct. You want to be on different rails than other parts, and looks like that middle plug can support 2 GPU’s all on its own, so it’ll be plenty good for a single card.