What you need -- as Sonusman said -- is an Analog-to-Digital converter. More commonly called an AD converter. To be specific, one with a SPDIF output (which is probably the most common format, so that probably won't be a problem).
There are lots of them. The cheapest reasonably ok standalone would probably be the Midiman Flying Calf, I think.
Usually, people use the AD converter that is built into their digital equipment (CD recorder, DAT deck, Hard-drive recorder, sound card). Typically, when people buy a separate standalone AD converter, it's because they want a really, really good special-purpose unit. So most standalone AD converters are really, really good, and quite expensive.
If you've already got something with an AD converter built into it (like a CD recorder or a DAT deck) and a digital out, you could probably use it: just run the signal into it and take the digital out. As suggested by Sonusman.
AES/EBU is another format -- like SPDIF -- for transfering a stereo digital audio signal through a wire. The thing you've linked to converts between the SPDIF format and AES/EBU. It doesn't convert between analog and digital. It's not what you're looking for.