We've all been there before: Your new DVD player or game console outputs a digital signal via only an optical jack, but your AV receiver only has a free coaxial connector. You need that digital signal to get 5.1 Dolby or DTS surround sound. Otherwise, you'll be stuck listening to two-channel stereo. Or the matrixed faux surround, courtesy of Dolby Pro Logic or Neural modes--nice, but why settle for that when you've sunk all this money into your home theater system? Thankfully, there's a workaround: Instead of opting for a new DVD player or a new receiver, you can purchase a small device that will convert an optical signal to a coaxial or vice versa.
One such device is the Tributaries AC100 Coaxial/Toslink Audio Converter, a tiny white cube measuring in at 1.6x0.9x1.7 inches. It's got two sets of coaxial and optical connectors on opposing Input and Output sides. Operation is simple--just plug your source into the In side of the converter, switch the lever to choose the output interface, and you're all set. There is one annoyance: that single toggle switch is set flush with the plastic exterior, so you'll find yourself needing a pin or a toothpick to make the appropriate adjustment. (In addition to converting a signal, you also have the option to repeat the signal being transmitted as well--useful if you're covering a long distance with two shorter cables.)
The AC100 utilizes a 7.5V AC power supply (included), so it will take up yet another berth on your power strip. Should you be using the unit to repeat a signal via the coaxial connection, no power is required (though you could accomplish the same thing with a two-dollar connector).
In terms of performance, there's not a whole lot to say about the Tributaries AC100 Coaxial/Toslink Audio Converter besides the fact that it works completely as advertised. But here's the rub: There was no discernable difference in performance between the AC100 ($50 list) and a similar RadioShack PCM/Optical Converter (about $20). (Unfortunately, it appears that the RadioShack device--catalog No. 15-1228--is no longer available online, though it may still be available at local 'Shacks around the country.) In other words: the Tributaries AC100 is a perfect solution for anybody who needs to convert a digital signal across disparate plug types, but going with a similar "no-name" alternative will likely work just as well--and save you a few bucks.