Don't worry, Trifid and I are good.
Like said, the Powerstream is both a 24-pin & 20-pin. You just clip on the additional 4 pins if you require a 24-pin connector, otherwise, just use the existing 20 pins.
With your system, I'm beginning to wonder if you would be better off with a 600w Powerstream. I really don't know. A 520w may be enough power; I'm just not sure.