>>Bruce, the odds are that these are the right and left channels for autdio input; you can confirm this with a set of RCA jacks and a Voltage meter - if they're inputs, the vlotage on them shouldn't change during sound playback.
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>I'm pretty sure you are correct. The little notes have left & right arrows next to them, and the manual has the text "For connecting power speakers to your computer" by the image. There is only one connector to connect speakers, as I said, I have that connected with a 'Y' cable to the PC-speakers - that can't be stereo with only one line, can it?

Sure, if the connector is split internally, left, right and a common ground is a not uncommon connecotor - headphone jacks, for example.