Ehmm...I'm confused. Define what you mean by controller? If you mean using the Casio as the sound source, then the Roland is the controller. You need to set the Casio to respond monophonically on consecutive MIDI channels. I can't remember how one does this; press the MIDI button, and RFM...Also check out the Casio hut at http://www.the-gas-station.com/
There are no plug in sound cards for it; after all, it's ancient!
I think you should also check out some books on MIDI.