You'll need the Airport Express, which I believe is the only one that has the audio out jack. Airport Extreme and Time Machine do not have the audio jack.
But I'm sure there are other devices out there, other than Beats by Dre that have the AirPlay built in that sounds just a good and probably the same price.
I know this is a league of it's own. But I have a Pioneer Elite VSX-53. I also have Mirage speakers. Obviously this isn't a small device like the Beats by Dre. But it does have a nice sound to it.
Google "best airplay speakers". There's a large list that range from $116 to $573. At least this way you don't have to relay on an external device to do the AirPlaying.