Product review (2 stars): Shocks not the problem
My Duet sport 2008 only has three attachments for a shock, although the tube has five!  After installation, the washer was leveled up and run.  It shook more than ever.  I believe that the concrete weight in the front of the tub throws out the balance of the frame.  I wedged hard rubber motor mount wedges under the left and right front sides, and two in the front.  That reduced the shaking quickly because it limits the occilations caused by the inertia of the weight.  This was a poor design to begin with and fortunately this has been the only problem with this machine.