Why does the new Focus System include an additional adapter (dongle)?

With a recent update (14), Apple has introduced a volume-limiting function on its iPods.  The result was not enough volume output to power the bone conduction of the Focus System headphones.  As a workaround, our technicians found that when a dongle was connected, the volume limiter was bypassed.

See the illustration below to properly connect the adapter (dongle) to the amplifier.