Of course you can add peripherals. I much prefer all-in-one package. Set up, plug in and play.
See... i allways prefered having 2 keybeds... Currently only have one, and in the market of adding a 2nd keybed, then its smarter to add a keybed with sounds...
So basically one could have both the Yamaha and Korg sounds, best of it, they really add to eachother... where one is strong, the other isnt.