Hi, in the manual, I managed to find this use for the external device, as you suggested:

"Outputting MIDI to an External Device
Some external music hardware devices require chords played in root position to drive them in real time.
An example of this is the Vocalist. It will let you sing into a microphone and harmonize your voice according to the
chords that are input to the device. Band-in-a-Box has the capability of outputting a separate channel with the chords
in root position to support such external devices automatically.
There are also settings such as complexity of chords, output channel, velocity, and note range. It will also drive “Real
time Arrangers” like the Roland RA series. The best way to accomplish this is to access the Options | Preferences
and select the [OutputCh.] button. You will then be given a window like this..."

But I have not found yet other uses. More advice would be appreciated.

Thanks,