Hi Frank, I was hoping you would join in this discussion! I had though about an arranger as an MFX plug-in (which are MIDI-IN to MIDI-OUT). This might be a better solution for those that use arranger functions only a fraction of the time. Having the arranger be the host would work better for those who used the arranger functions most of the time. I think BIAB is on the right track, except it is non-real-time.