Hi David, I appreciate your quandary. I recently designed and built out a co-working space, called COspace, here at the Univ of Toledo’s business incubation complex. The space i had (5000sqft) was all uninsulated concrete, steel and glass-highly reflective and amplifying.
So, depending on the size of the space you have to work with, and the distance between individual task desks/cubes, there are solutions that help. Obviously, carpet is the first consideration. Good, rubber backed low-rise carpet squares seem to be popular. You don’t need to do the whole floor for this. Also, there are noise mitigating materials that can be hung from the ceiling, depending again on the space you’ve got. Those can be seen at http://www.armstrong.com/commceilingsna/. And lastly, I also had a previous life in music production, so you may find sound insulation foam panels of use. Those can be found many places and even the less expensive work well in volume.
Otherwise, my biggest recommendation is HEADPHONES!
Best of luck.