Sorry Brandon this is incorrect. The relation to ro on seawater is not relevant. The sodium added by a softener is by removing calcium and magnesium which are more likely to clog the membrane over time by calcifying. So you are not adding much overall salt to the water. The RO membrane has no problem removing the sodium.
I also wouldn't worry so much about the pressure. Yes it would help to be higher with output and a slight increase in quality of RO water but if he is burning through an entire DI cartridge with a few buckets of water there is a bigger problem with something getting through that increased pressure won't solve. Probably the CO2 issue..
I looked at several sources and they all say the softener should be before the RO unit.
from
https://www.secondwindwater.com/reverse-osmosis-with-water-softeners/
Water Softener
A water softener will protect your reverse osmosis system by
removing scale-forming elements like calcium and magnesium, before they ever reach it. In the process, water softening can add slightly higher levels of sodium to the water. (How high these levels are depends on how hard your water is).
This is where reverse osmosis comes in.
Remember what we said about being better together? Your reverse osmosis system, which purifies your water, will also remove the sodium added to softened water.
