So, if you have an average player (left hand chords, single finger melody) on a Yamaha E-213, and you compare that performance with the same player on a T4 the results are not better, and more pleasing??
I think he/she will sound a hell of a lot better on the T4.

As to stereo vs mono...I would NEVER use Mono on a arranger keyboard, or even a synth. I tried the Kurzweil K2600 once mono...sounded like crap...then to quality stereo monitors...WOW..
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Lee S.