Band in a Box has a few flaws I don't like.
1) You can't assign parent scale to chord progression, it seems you should be able to assign melodic minor, harmonic minor, harmonic major or simple things like dorian or lydian to progressions, otherwise how can it know what notes to add.
2)no support for quartal harmony
3)no support for quartal harmony in odd scales like melodic minor or harmonic minor.
4) Voice leading is not very good in many cases (want oblique, and contrary motion)
4) b5 substitutions taken from corresponding melodic minor scale, you can fake out Band in a box by typing aFlat maj\min over G for b5 dominate chord.

so Dm, aFlat maj\min over G, cmaj7 would be the ii V I
Many of these things I have figured out how to do, on my own

5) I don't like real tracks I want MIDI tracks, MIDI is more flexible for professional tweaking

I have a lot of good ideas but I just don't want to give them away for nothing.