Just to be clear doing 'So What' in Band in a box is a hassle, the melody is in the bass for part of the song so U have to edit the bass track, so if U use real tracks U have to delete audio? this is nightmare, deleting MIDI is easy, U can use band in a box for most of the song and delete the part where melody is in the bass. U can edit velocity (so that volume is right) because it midi, U can replace the keyboard with real Quartal harmony it is not that bad but if your in the audio world it is total nightmare. This is why real tracks should be convertible to MIDI, MIDI is way more flexible in terms of computational editing, also U should support more advanced concepts like Quartal Harmony and different scale types.