I suppose you could combine them into one but it would be easy to find a high wattage power supply to fit all needs.
And combining them into one would be rather difficult and involve completely disassembling them both since you would need to wire all the rails in series.
An easy alternative would be to use on PSU for the motherboard , RAM, CPU and one video card and use the other for the remaining video cards. Or whatever split best suits your needs. And if you read the article, this is exactly what they did. I don't think they made it clear the split they did with the cables though.
Basically, take one, plug in stuff. Take the second one, plug in more stuff.
So if you read the article carefully, they didn't "combine the power supplies", they just used plugs from both for different components.
All I could find was an adapter that took two of the wires from one PSU and the rest of the wires for the other for on the motherboard connector. Considering they had a 450W and a 1200W good quality power supply, I doubt they did this.
I'm not worried about the price of a high wattage PSU, I want to reduce the demand of each PSU to 700W, and get a UPS for each, because to get a descent UPS to support 1300+W can get pretty expensive. I plan to use 2 of these UPS :Cyberpower CP1500AVRLCD UPS, to keep my system safe. You guys think that this will work?