If i were you i would buy another ro housing, then buy 3 new 150gpd membranes ( got mine from Daqua ) also add a booster pump ( got mine from wcw ).
This will give you a set up that makes good quality water ( may not need di ) and produce it at a reasonable rate.
This is the set up i have, it takes my tap water of 414 ppm down to 003.
I still run it through a 11ltr di vessel, but i havent changed the resin for over a year .