I bought the same press this year also. We were using 3-4 cups for 10-15 gallons. It works like a charm. The DE cakes came out at about a 1/4 inch think when we finished. We premixed it well and recirculated it till it was all in. It was expensive? yes, but was it worth it? hell yes!
One thing I did add was a SS ball vale to the outlet port on the 1st plate. Keeps the syrup from spilling out when you take off the hose.