Due to the way that Cartesian Impedance mode works, there is no code to set the axis limits without writing your own class. Are you keeping your robot stationary, like in the Impedance mode seen in the lbrExampleApplications folder? Also, what is the purpose of running Impedance Control Mode with low enough resistance to be pushed to the axis limits? (If it is to emulate hand guiding, that can be quite dangerous, and you should figure out how to get the actual hand guiding code working...) You may also try a different Impedance mode called JointImpedanceControlMode(double A1, ... , double A7). This mode will allow you to set axis limits via the setMaxJointDeltas() command, however, the robot will not have the "spring like" motion in the cartesian space, rather each joint will have its own spring motion. Again, make sure to evaluate the application you are creating to make sure this is the correct implementation. Also the browser is VERY helpful in situations like these, and an easy way to access it is by hovering your cursor over the implementation you wish to learn more about (in this case, CartesianImpedanceControlMode) then clicking the globe icon at the bottom of the window that appears (see attachment).
Hope this helps!
-Alex