audioI have a TV with optical digital audio out (S/PDIF) and 5 old speakers with bare-wire cables. How can I connect them? Probably I need some kind of digital-audio converter. I'm looking for a cheap solution.
bare-wire: I'm not sure that this is the correct name. There is no jack or other connectors at the end of the cable, just the bare wire.
I believe what you're looking for is an A/V or Home Theater Receiver. This will function as both the digital audio converter and the amplifier for the speakers, as well as performing input switching and a host of other features. Receivers are very common pieces of electronics, and you should be able to find a decent selection at most electronics stores.
This may not be a cheap solution however, entry level receivers(with 5.1 channels and digital inputs) seem to start around the $200 price range, and goes up and up with quality and features. You can keep an eye on the used market though, since you're only looking for S/PDIF inputs you can get a model that is several years old that will do just what you need.
Before you make a decision though, Why have you chosen to output over S/PDIF from your television? What is the source of the audio? If you were to add a receiver to your setup, ideally the sound would never make it to the television. You would send the audio directly from your devices(game console, cable box, computer, etc.) to the receiver.
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