desk top speaker hook up with a Samsung P 2370 HD monitor

I bought a Samsung P 2370 HD monitor to be used as a HD television in my bedroom. I also bought the Cyber Optics CA-3602 desktop speaker system to hook up to it. However, when connecting the single male plug from the speakers to the headphone jack in the monitor, only the two small desktop speakers work, the sub woofer does not. I spoke to Samsung, and they said I need to get a cable for the digital audio port to hook to the speakers, but I cannot find a cable that is compatible. Does anyone know where I can access such a cable or have another solution? Many thanks.