Chas, Wrong....with an arranger on top you have all the controls on top just like organ, IF you just use a dumb lower MIDI kbd. The problem arises if you use a lower that is not dumb...then you need o get to the controls of the lower and cannot put the upper literally right on the rear of the lower, on a slight angle and overlapping a little. I do not need any control on the lower manual, well, maybe joystick or Mod, pitch wheel, which are now usually in the way.....just keys. 61 will be just fine with my SX-900. Still looking for the ideal lower kbd to add.