I used to use an XK as a controller when I played for a country music band in the early 90s. It was an excellent and small controller with a responsive keyboard best for playing Hammond organ parts (perfect for glissandos). The programming was simple yet very flexible with zones, velocity, patch changes (up to 3 I think) and even an arpeggiator. Make sure you have the original power supply -- I don't think the built-in circuitry is regulated and too much/irregular voltage may kill it. They are run on a Motorola 6809 if I remember right. Another favorite feature is the pitch bend/modulation levers. They are also assignable, spring loaded, and pull towards you which makes it easier to emulate guitar-style vibratos using pitch bend. Get one if you can find it -- they usually aren't more than $300 on eBay.

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"Music so wishes to be
heard that it calls on some
to give it voice and some to
give it ears." -- Fripp