You would have to have an additional amp, since the amplifier in the 580 is specifically "married" to the 580's speakers. The first question is, do you want to send standard stereo signal (left and right channels) to the rear speakers, or use some sort of processor to create a delay or take advantage of Dolby decoding for rear channels? If the answer is the latter, you will also need an add-on processor -- but at that point buying an affordable surround sound receiver probably makes more sense (because you'd get your amp and processor together at a better price than if you buy separately).
But before you buy any of this stuff, we have to ask, have you had the ZVOX 580 for a long time, or did you just get it? We suspect that after you live with it a while you might not feel that you need rear speakers....but that's just ZVOX guys thinking...
Good luck!
zvoxaudio.com
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