An arranger only requires that if you intend to control styles or use the "Auto Bass Chord" faculty. The D-Deck is kind of a hybrid with fewer chord recognition modes than a Tyros/Genos. But a true organ doesn't even have styles or Auto Bass Chord. If you start with a BK-9: turn the melodic auto-accompaniment OFF, split the keyboard, and add bass pedals, now you can play chords any way you want, just like on an organ. Play it through a Leslie cabinet, and with your back turned I bet you couldn't tell!