The hyper64 does output stereo sound. The newer version of the hyper64 outputs stereo on the jamma connector. On the older version you have to use a separate 4-pin stereo connector on the front of the unit (the smaller white connector).
If your jamma harnes in your cab is wired up for mono, you can just simply run wires directly from the 4-pin stereo connector to your speakers (of course you have to disconnect the existing wires from your speakers).