Do a total of four Split Circulates, except that when you become an In-facing Center do your next Circulate to your diagonal opposite position (crossing over into the other Box). Exchange The Box can be fractionalized into fourths.
Traffic pattern: when crossing to the other Box, stay outside of those who are still in their original Box. The In-facing Centers lead the Exchange and, from a normal setup, everyone else in their Box can follow them.
From Parallel Waves (In-Facing Centers lead):
From Columns (In-Facing Centers lead):
Dancing hint: Those leading the exchange should raise a hand to identify themselves so that the other dancers in their Boxes can follow them.
See also Exchange The Triangle [C3A].