Thank you

I'm slowly discovering there is a delicate balance between having non-scaling, non-corrosive water, and optimizing the flavor of the coffee; in my particular case, I'd argue the two are mutually exclusive. I'm using RO water spiked with sodium bicarbonate, but the water is, for lack of a better description, too 'neutral' or 'sterile' for my liking; I much prefer the taste of my filtered tap water, but it is very hard, close to 350ppm. I'm thinking of adding a little tap to the RO, or perhaps mineralizing it another way.

Have you tried mixing RO and tap water? Works pretty well in my experience.

Not yet, but I'll get there (I know that I'll need no more than 1/8 tap water to keep the hardness at a reasonable level). I'm going to experiment with Third Wave water first and go from there.