Hello. That tech is on point. The GTX 680 and ATI 7950 will both utilize two AUX power ports.
You don't really have to run a wire from the optical area to the PCIe slot area. Instead you can use the SATA connection from the Drive Bay 3 or 4. You can get a SATA to 6-pin adapter.
To the GPU, I would connect one 6-pin from the logic board and one 6-pin fro the SATA adapter.
To the HDX, I would connect the 6-pin straight from the logic board. The HDX is worth more money, so it's better to be safe with that.
For example:
https://www.amazon.com/UGREEN-Sata15...dp/B01EUSZ0BQ/
The other route will be to connect an external power supply, which can sometimes be complicated with wiring.