Your CRSpotless has a capacity of 84,000 ppm??? Wow, that's
huge, and I think probably not correct. If so, then the CRSpotless cost effectiveness makes this whole discussion of putting together a DIY system moot. I'm just about positive that the 100 gallons of capacity from
DIW-10 Spot Free Wash System - Deionized Water Maker - CRSpotless.com is figured at 7 grains per gallon which is the national average water hardness. The filters used in that unit are ten inch units, and the ones I'm using are 9.75 inch filters. The ten inch ones having a 700 grain capacity (per two filters) falls pretty much in line with the 9.75 ones having 600 grains capacity (per two filters). I'm pretty certain that my figures are correct. Plus, you're stating that your system has a 375 gallon capacity, which doesn't agree with the stated capacity from their web site of 100 gallons.
Anyway, here's the info for the higher flow and capacity system I was thinking of:
The 3 gpm capacity system consists of this filter:
FPMBDIR-BB-20 which is $125.00 and has a capacity of 1900 grains (about 271 gallons at average water hardness of 7)
And the GH400 housing from this page:
Garden Hose Filters with Higher
which is $118.00.
Total cost for this setup is $243.00, and would flow well enough to feed any home PW.