Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Matrix Mode
GV_BOX_MODE
Parameter: Use Deformed Points
GV_BOX_USE_DEFORMED
Parameter: Box Minimum
GV_BOX_OUTPUT_POINT_MIN
Parameter: Box Maximum
GV_BOX_OUTPUT_POINT_MAX
Parameter: Box Size
GV_BOX_OUTPUT_POINT_SIZE
Parameter: Box Point 1
GV_BOX_OUTPUT_POINT1
Parameter: Box Point 2
GV_BOX_OUTPUT_POINT2
Parameter: Box Point 3
GV_BOX_OUTPUT_POINT3
Parameter: Box Point 4
GV_BOX_OUTPUT_POINT4
Parameter: Box Point 5
GV_BOX_OUTPUT_POINT5
Parameter: Box Point 6
GV_BOX_OUTPUT_POINT6
Parameter: Box Point 7
GV_BOX_OUTPUT_POINT7
Parameter: Box Point 8
GV_BOX_OUTPUT_POINT8