A bit more info on your tandem and riding style/conditions would help.
Do you have your bars too low and consequently to much pressure on hands?
Have tested some of those 'magical' gel things under the bartape, and found them to be wanting greatly.
Agree with Ritterview that a wider tire would help; and a full carbon fiber fork would greatly reduce vibration and even lighten up your bike.
A suspension fork is heavy and will suck up some shock. Have you priced a tandem-rated $uspenSion fork lately?
Pedal on!
Rudy and Kay/zonatandem