I managed to connect two 8 pin cables provided with the PSU to the 2 ATX_12V connectors and pass them out that tight spot. Not as graceful a run as what you had suggested. The cables weren't long enough to go around from the front to the back and to the front again, so I had to leaf them through a tight opening near the edge of the MB. A little too close to exposed pins for my liking. No love for this case. The amount of bulk from the pwer cables has resulted in me having to remove the SATA drive bays. Not sure where I'm going to put a drive now.
Anyway, one of the two cables has been successfully connected to the PSU, however, both cables are NOT the same. Although an 8 pin connector that fits in the PSU next to the other, the retaining clip is too big! It's double wide where all theothers are just single clips. There is no where on the PSU to connect this!!!
If this doesn't kill this project, I'll be surprised. The amount of work it takes to do any work in the case, with the huge 3 fan cooler and rad, is crazy. I have to take the top off the case and lift it off with the radiator and fans to get access to the headers and connectors along the top edge of the board. And it's not very cooperative.
Such a subtle difference you don't care to look. It connected to the motherboard with it's single clip connector. I assumed, like the other, that the ends were the same.
Do I need both??