MGX file extensions indicate that a multichannel MIDI file is present on either Melody or Soloist track. This occurs if an external MIDI is loaded into BIAB and then saved as a BIAB file. The below is from the 2019 manual.

Originally Posted By: BIAB_2019_Manual
You can open an entire MIDI file into Band-in-a-Box. The chords will be automatically interpreted by the Chord Wizard and the MIDI file will play and display on the Melody track. A “silent” style will be loaded so you will only hear the MIDI file. When the file is saved, the extension will be MGX, allowing you to easily identify the BB songs that you have that contain entire MIDI files.


To elaborate on the above...

When a MIDI file is opened in BIAB, a 16-channel track-type is created on either the Melody or Soloist track depending on where the MIDI file is sent.

In the BIAB program, this occurs in the background. As far as I'm aware, the VST plugin does not support a 16-channel MIDI file on a single track like the program does.

As mentioned above, from a user's perspective, the MGX extensions indicate that the BIAB song file is MIDI on either the Melody or Soloist Track (with no style playing). To transfer this MIDI to a DAW just drag the Melody (or Soloist) track across to the DAW.

When I drag across in Reaper, I'm asked if I want the multichannels split onto separate tracks (to which I say 'yes').

Hope this helps.

Regards,
Noel

MY SONGS...
Audiophile BIAB 2025