Bernie my two cents.
The more stuff I have the more I have to carry. But even more important, the more equipment I am using the more I have to be concerned with. There is no doubt about how a preamp can add to your sound. They use them color the sounds before it is amplified.

At one time I was using a mixer, a BBE sound maximizer, and an EQ. besides the instrument volume controls and EQ. With your equipment nothing is needed but a good microphone. (My opinion)
Your new korg keyboard has volume controls and EQs for the instrument and voice. They created a keyboard that does it all.

If you had thoughts about adding another piece of equipment, or more microphones, that changes the story.

Hope this helps, John C.