I have the aquatech 8800, w/2-400gpd membranes. It works good for me. Are you saying you have 200-250gal of sap per batch, But you have 700gpd membranes or multiple membranes that equal up to 700? I dont recall all the specifics on how these things work but I can tell you for me I do about 60-100gal/batch and cycle it to about 7%. Not sure if that helps. I seem to remember something negative about the reviews I saw about auquatec 6800, can't recall.
2019- RO
2018- 25 taps made 8 gal syrup.
2017- 25 taps -built a 2x3 flat pan, and a fuel tank arch for it. 335 gal 7.34gal syrup.
2016- 15 taps, 4.3gal syrup boiling on cinderblock arch 3 roasting pans, 1 redneck trash can with a pot, and a turkey fryer.
2015- 4 taps 44 gals of sap made 2.25 gal of lite syrup.