You only take two doses of ES (okay, that *is* two too many!) - I guess the Oxypowder is used to clear the way initially. I took the SuperPhos, but it was my first flush and I didn't have anything on handand had to buy something.
I'm going away for the 4th of July weekend and that Monday is when I'm supposed to start the SuperPhos for my next flush, but I was planning on getting some malic acid to take with - don't want to cart around a bottle of liquid. As long as you are taking something to break up the stones, you should be okay.