I have a softener before the RO (4040) and I can have the tap right down so a trickle of waste at around 500-800ppm, and still low ppm for pure, but coming out more quickly.
(BTW: Water in 160-180ppm.)
Don't know what this is doing to the Ro though, I guess as long as I open the valve fully once regularly and flush through it should be ok, but correct me if I'm doing it all wrong?
as long is there is no salt there is not a problem.
I got told this from a guy that is clued up, I will try and explain what was said.
softener make water bigger, when hitting the ro it is like 50p and pennies 50p are forced through ro and pennies in waste hope that makes sence.
I got the straight off when told (and Jerry again you are a star, fosters

)
when i did a test on water after softener my tds meter went mental and said x10 997 and it scared the life out of me, as said it in simple terms makes the water bigger, add a booster pump in with this and the results are FANTASTIC
Ian