Don't be satisfied with 0 out. Make sure you keep track of the RO membranes performance too as it is a very important part of the operating cost of the unit. If your membrane is giving you 96% rejection instead of 98% rejection your DI resin will last 1/2 as long. Thats hard to believ but its true, a 2% difference in membrane efficiency doubles DI life. Replacement DI can add up in a hurry and make inexpensive units into expensive units pretty quick. People don't want to hear it but cheap e-bay filters can and will cost you more in the long run.
That aside, I applaud you for providing the best water quality for your inhabitants. Water is the single largest ingredient in your system so why not take control of it yourself and provide quality you are sure of! Mine is 836 TDS in, 7.7 after RO only and 0 TDS out.