What are the key differences between Audi's standard Quattro and the new e-Quattro systems?

I've been researching Audi vehicles and have come across two different versions of their Quattro systems. Can someone explain the main distinctions and advantages of each one?

The standard Quattro system is a traditional all-wheel drive system, using a center differential to distribute power between the front and rear wheels as needed. The new e-Quattro system, on the other hand, is a hybrid system that adds an electric motor to the rear axle for instant torque and improved efficiency. Both systems provide excellent traction and control, but the e-Quattro adds a boost to acceleration and improves fuel economy.