Hi George!
I am not really into Yamaha arrangers, but here's what I'd like to see in all of the arrangers: as many asignable buttons and sliders as possible.
And, if they would make a stick pitch bender / modulation rather than wheels, I might buy a Yamaha.

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Yamaha S770, Studio One 3, EMU 0404USB, ESI, ATH, Dell. And others.