My water is harder than yours! I use it as is from the tap. I've got pretty much South/Central/North American plants and most seem to be thriving. Like a jungle I'm afraid. Some of them, Potamogeton gayi, for instance have been slow adapting, but most do just fine. Your RO blending should work out fine. You can check out my profile under View User Tanks for more info. I had melting initially with some plants, but was quite surprised how most came around.
I've got a copy of my water report if you'd like something to make you feel better about yours. LOL
What did the catfish say when he ran into a concrete wall?... "Dam!"