Turn the boards over so they bow up in the middle, instead of on the ends, and put a little weight on them to keep the flat against the concrete.
Kind of sounds like your concrete may be high on the moisture vapor emissions.
My concrete is flat and dry (over 8 years old). I did a test to see what it would take to flatten out a 33.5" board which is bowed about .220" in the middle and it took 23 lbs of pressure. Obviously, the longer boards, though bowed even more, take less weight to flatten. I finally received a reply from the manufacturer, and here's part of what was said: "...regarding bowing in 3" Hickory Character grade. Our manufacturing process does allow for up to a 1/2" upward deflection in the center of flooring when ends are in contact with floor, providing the bow is "soft" and can be flattened with light to medium pressure."
I have requested that they define "light to medium pressure". I am sorry for wasting all of your time on this forum, but I have a nice, quality house and don't want to cheapen it if this flooring doesn't install well. I really do love the look of the wood and milling quality, but the bowing has got me puzzled. What would you pros do in my situation? I had this stuff shipped from the Midwest to Idaho (local distributor wanted way more) and to return it would set me back both financially and time-wise.