That is a typical result. Only the Ca, Mg, and Na results really shift. Ion exchange softeners are very good at their job.
PS: that unsoftened water has fairly high Mg. There is no need to ever add Mg to that water, so don't consider it. RO water would be a good addition to the brewing tools...just to reduce that Mg content. The rest of the profile is OK...well excepting for the alkalinity that needs to be neutralized!
Thank you for your insight Martin, your great article in the Nov/Dec '13 Zymurgy is what got me interested in looking into my brewing liquor. After working with the numbers on your spreadsheet I plan to use at least 50% RO from now on in my brews. So to help with the alkalinity, would you recommend using acid or just start with more RO?
P.S. I made a couple of beers with the softened tap water... no wonder my IPA tasted a bit harsh and salty! Lesson learned.