They are adaptable, but I remember reading somewhere that the recommendation for acidic water it has to do with how ammonia is mainly in the form of non-toxic ammonium when the water is acidic.
That combined with that fact that some people seem to recommend keeping them (or at least used to) in tanks with no filters, so that lots of detritus could build up for them to feed on and so baby shrimp wouldn't get sucked in (no idea why they wouldn't just use sponge filters, or put a prefiler over a power filter.
I would personally go half tap and half RO water and skip adding anything else that messes around with water chemistry, just make sure the tank has a mature filter, and some plants, wood, leaves...that sort of thing so the shrimp have something to pick at.