That gives a number of choices to suggest....
What about a Ketron and a Midi-controller keyboard, M-Audio or something?
You solved demo 4... Ketron SD1000 played via M-Audio Code61..

Now what keyboard in demo 3..?
Demo 1 was the SD1000 and One man band 12, playing a Tyros style.
Demo 2 was the SD1000 playing a SMF..