FWIW, in regards to the stoker seatpost, and I have not tried nor has my stoker tried the body float, but a properly sprung Thudbuster LT seems to be the go to item for stoker comfort.
Consider the stoker seatpost may be you salvation to riding a tandem. As a captain, you only experience a portion of the bump from the rear wheel. The stoker gets all of it, seldom stands and sees nothing coming.
Even with the LT Thudbuster, there were many times you could hear the stoker take the hit I did not call out or was not realized during a corner.
All the best with your new machine. We had a USA made 98 Cannondale MT 3000. That machine was very well adapted to tight single track. Sometimes we wish we still were riding it, but quickly realize we are better off on what we have now.
PK