Fosters your paying for the name..
More filters means more filters that is it... the more filters before the DI
resin just help to remove more waste in the water not create more waste water.
You will have the same amount of waste water it runs about 4-5 to 1.
Low water pressure can produce more waste that all Im saying.
Trust me when you want water you do not want to wait 3-4 hours to get 1 gallon.
Ebay is the place to go....
For 200 you can buy a great unit on ebay and have money left over for something else like more LR
or another fish.
Do a search on the site there are other posts on this subject. We need to save money where we can in this hobby.