The parking brake has 2 modes. When the ignition is on, activating the parking brake uses DSC to apply the regular brakes (that's what you're experiencing). When the ignition is off, activating the parking brake activates the parking brake actuator which pulls on the Bowden cables to set the parking brakes.

If you have the ignition off and activate the parking brake, can you hear the actuator working?

Is the emergency release cable installed properly on the new actuator unit?