This is a variant of an earlier post, this time using JustePort to send the audio to an Airport Express.
Save this script as 'airradio':
then run it like this, for example:
TMP="/tmp/radio-`perl -le 'print localtime()'`" mkfifo $TMP cat $TMP | mono /usr/local/bin/JustePort.exe - 10.0.1.1 & mplayer -playlist "$1" -ao pcm:file=$TMP -prefer-ipv4
(10.0.1.1 is the IP address of the Airport Express)