While the S3 has a midrange sub-enclosure, the S5 does not.
This statement is false. The S5, just like the Q3, Q5 and Q7, have a rectangular midrange enclosure, made of aluminium. Both the S3 and S7, have a new, eliptical enclosure, which according to Magico, brings some benefits.
Without the sub-enclosure, the S5 midrange would be blown out of its chassis, on a first heavy bass note.