Traditional room correction corrects each speaker independently. MIMO room correction treats all speakers as a single coordinated system, using constructive and destructive interference between speakers to control room modes more effectively than any single speaker could alone.
MIMO is especially effective for bass: multiple subwoofers placed in different room locations can cancel each other's room mode excitation, resulting in much smoother bass response than a single subwoofer plus DSP. High-end systems like Dirac Live Bass Control and Trinnov use MIMO approaches.