Perhaps this new auto trim system bypasses the stick shaker because it "thinks" it is handling the approaching stall/misiterpreted nose up attitude.
Still it is a matter of turning off the electrical inputs. One of the cutout switches disables the auto pilot trim and the other the manual trim. Based on the old system, a manual trim failure (stuck trim switch etc) would be obvious as the trim would operate rapidly but an autopilot induced failure could be much more subtle.