Uncle Dave

Now, I have the internal electronics circuit of 740, and so I am able to clarify the question of rear outputs control volume:
Indeed, observing the electronics, it's clear that was intentional from Yamaha to let the internal speakers as monitores affected by the panel volume button and not the rear outputs. (For the rear outputs all we know that the foot pedal volume control that).
And so, it is very easy to change the default wiring from Yamaha. It's enough open the keyboard and move two wires from two points of the circuit, before the volume control knob, to other two points whose are the middle points of the control volume knob (this is as normaly, made by two variable resistores on the same axis).
The printed circuit board for this, is independent of the CPU, ROM(s) board, and very accessible.
However I think Yamaha is right and I have not changed the default.

Regards
Carlos Rodrigues