What's the best thing to use for audio output to a stereo for my MB, cable or airport? Is it only possible to use the airport for streaming music from iTunes?
To use an Airport, you need an Airport Express router. They are a good solution if you need a router and your stereo is far from your computer. Otherwise just use a Line Out mini-plug to RCA cable.
If your stereo has a digital optical audio in, then I would suggest the digital optical audio adapter for the MB. Quality is top-notch. Cheaper than other options too.