Here is a complete (and accurate) explanation of how the S-AWC works in the Evo X as explained by Mitsubishi Canada.

UNDERSTANDING SUPER ALL-WHEEL CONTROL (S-AWC) – LEVEL II
The Super All-Wheel Control system utilized in the Lancer Evolution represents the pinnacle of Mitsubishi Motors' all-wheel drive technology. The Active Front Differential (AFD) of the Outlander XLS is replaced by two stand alone technologies – the Active Center Differential (ACD) and Active Yaw Control (AYC).
The ACD found in the Lancer Evolution manages the front to rear distribution of torque based on available traction. It also features an integrated helical limited slip front differential which directs torque to the front wheel with the most available traction.

What sets this S-AWC system apart from anything else in the market is the AYC. AYC enhances the performance capabilities of the Lancer Evolution by comparing where the vehicle is going versus the path intended by the driver.The AYC determines the difference between the two by comparing real time data from the yaw rate sensors and comparing it to steering, throttle, wheel speed and braking inputs.
AYC also plays a key role in the enhanced performance capabilities of the Active Stability Control and Sport Anti-Lock Braking systems, increasing braking force on the inside wheel during understeer and on the outer wheel when oversteer occurs.The braking force control feature of the AYC system works in concert with the torque transfer capabilities to deliver enhanced cornering performance and vehicle stability.
The net result is seamless and effective control of the vehicle whether the driver is accelerating, decelerating or turning.
The Lancer Evolution offers three operating modes:
Tarmac – Provides a rear bias for improved performance under optimal conditions.
Gravel – Splits torque equally to ensure balanced handling characteristics under lower traction conditions.
Snow – Provides a front bias for more forgiving handling characteristics under slippery conditions.
Competitive Note: The Subaru WRX and WRX STI don’t have the torque vectoring capabilities of the Lancer Evolution.