Airfoil from Rogue Amoeba $25 is worth the money, and more.
I had been looking for this product ever since I hooked up two stereo systems to two Airport Express units, whilst at the same time getting addicted to Pandora.
I will let the site explain what the product does:
“With Airfoil, you can send audio from…
…RealPlayer, Windows Media Player, QuickTime Player, and other media players to the AirPort Express.
…Pandora, Last.fm, and other web-based applications to the AirPort Express.
…audio devices like the RadioSHARK to the AirPort Express.
…Dashboard widgets, such as RadioTuner and RabbitRadio to the AirPort Express.
With Airfoil, you can send audio from almost any application(1) to the AirPort Express.
Airfoil also adds the fantastic ability to send audio to multiple AirPort Express units at once. It’s now possible to send audio all around your house right from your computer. Don’t spend thousands of dollars on expensive solutions to get your audio throughout your home. “Wire” your whole house wirelessly, using AirPort Express units, and give your audio wings with Airfoil.”
What I will say is that it does everything that they say it will, with only a very slight “delay” when streaming through two Airport Express units. It comes over as a very slight echo, not an issue at all with music but it can be a little disconcerting with a podcast.
With respect to video this is what they say:
“I should point out, Airfoil is -not- suitable for use with video, that is playing video locally and audio remotely. The Airport Express buffers audio for 2-10 seconds, so video plays back well before audio. Because of this, it’s not recommended for video use.