Diki and others..
The stereo / mono issue can be a real problem..

I too with every chance I get prefer and play in stereo..Fortunately my keyboards sound good in mono and better in stereo.

There are situations[venues] we play that we have no choice but to play in mono..As an example..The AC casinos have very elaborate sound systems[$250,000]...because of the facility design, the system is designed basically as a mono system.

I play several clubs with great systems that only allow the audiences to hear mono...Hence lies the problem, especially Yamaha, which I believe relies heavily on stereo effects to give it's sounds character..Possibly Korg may have the same problem..they also rely on effects to broaden their sound. Maybe not as noticeable as the Yamaha line..

I think even the Roland stereo samples[as my DisCover5 and all the new Rolands], may suffer in mono also, but the sample wavs seem not to rely on the effects to make the voices sound great..

As I have mentioned several times I am not knocking any one instrument..just trying to point out situations where a great sounding board may not work in the real world because of "modern" technology.