I disagree. The components of TDS are often way beyond a simple measurement of Carbonate or Ferric/ferrous hardness. They may be the result of toxic cations especially at 2700 ppm!!!. You would (the homeowner) be accepting bad advice to just go ahead with a simple system.
As I said befoire its a chemistry problem and until you know the components of the water were all just guessing. I dont like gessing about whats in my water but many water treatment companies really dont care about your health, they care about your monthly service fee.
In several countries weve used dual water systems where the system is bifurcated for the potable component being treated to a higher (and safe) level.
Anyway, if the TDS were a simple hardness that was more than carbonate, it could be iron and manganese and the EPA guidance for manganese is less than 6PPM (manganese is a toxicant that can be associated with neural lesions. Im no water chemist(I was a REE chemist) but I dont accept some water treatment company telling the homeowner that some off the shelf unit will treat an unknown dissolved load that reslts in a TDS of 2700ppm withot knowing the components. That is just total BS. Some constituents (like lead can dissolve and stay dissolved in low pH water and shoot right through). As and Pb are sometimes naturally occuring components of certain aquifers (especially shallow aquifers of the West coast areas and New England glaciated terranes.
Reverse osmosis will need a pre conditioning and pH adjustment bt will take care of most of the TDS before it gets to your kinetico.
My opinion is that the second water treatment lab was being accurate, its a potentially difficult treatment of 2700ppm TDS. You should contact a" professional /commercial treatment company" that isnt just trying to sell you a system without more lab information.
Remember , its not a matter of cost, its a matter of what your health is worth to you. Water borne toxicants are a silent health problem all over the US where ground water is in use.