iRock wrote:1/4 headphone jack
Well that could be a stereo jack and if you have a stereo 1/4" plug (if it has 2 black bands around it it's stereo, one black band is a mono plug) then it would be possible to split that cable into two separate mono 1/4" plugs and plug it into stereo to your MPC
However, the stereo signal on such a keyboard could very well just be a mono signal but sent to stereo -- meaning that the same sound is going through both L and R channels for a kind of faux-stereo effect, but it's still mono because it's the exact same signal over both channels.
If that is the case, then there's really no point in recording that Casio keyboard in stereo, because it would just needlessly double the polyphony of the sample. In this case it would be better to record in Mono, which still allows you to have sound coming from both the L and R channels, but it is the same sound duplicated. But since it's mono it will only use up one voice and will also be half the file-size of a stereo sample