I have just acquired a set of Behringer MS20 speakers.
They work perfectly when connected to the normal line out jack on my PowerMac G5 however I was hoping to use the optical out on the G5.
When I connect the speakers using a toslink cable to the G5 I get no sound. I have checked the sound prefs and set it to optical out in the output tab and I've got the cable plugged into the upper of the two optical sockets on the G5 (which is the out one according to the manual and the writing next to the port).

Any idea what I'm doing wrong?

Suppose the first thing would be to check it's actually working at all - I'd start up iTunes or whatever and play something then unplug the toslink cable from the speakers and 'aim' it at your hand see if there's actually any light being sent down the fibre.

Jon

First thing I did.
There is definitely red light getting to the end of the cable.

Hmm.. OK. So then it's probably either silence is being sent or the sound data that's being sent is in a format that the speakers can't decode. Do you perhaps have a home cinema amp you could lug round to the mac (or vice versa) to give that a try? Most cinema amps will tell you on their front screen what format the sound data is in when they receive it. I'd expect it to be 2 channel PCM but it could be AAC or something.

I had a quick look on mine and there's no controls at all - no way to tell the mac to use a particular sound format. That could be... irritating.

I appear to have remedied the issue.

The speakers need a 24 bit/2Ch sound source. The Mac was outputting 16 bit/2Ch sound.

Confusingly the settings to change this aren't in the Sound control panel but in Audio MIDI Setup (in the Applications/Utilities folder).
Once I changed that the speakers started working.