There will be no difference in tone or effects. The only possible hiccup will be that if you raise the master volume level, keys and vox will raise together. In most cases, this is desired, but if you need to adjust one, without the other - there are dedicated knobs that can do this on the face of the keyboard. The only scenario in which I'd use the separate outs would be if I needed to EQ or add effects outboard. Since you run into a flat input that is summed with the other inputs, I see no advantage at all. You be the judge, but Korg has so much processing power built in - I think you'll be fine with just a direct line out from the KB.