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I think you would need to look on the 'Control Unit' which is often mounted on the underside of the left hand end of the keyboard, and is a flat electronic device box, with a number of jacks and outlets on it... the one labeled 'OUTPUT' or the one labeled 'OMNI SYNC' and 'OUT' would be appropriate, but unfortunately those aren't really headphone jacks. They come in Left and Right, as opposed to Stereo as is normal for headphone jacks. However, they can be used.