Karl's Ices works with jack, I have it compiled on both Linux and OS X,
although the OS X build don't perform too well. It only streams vorbis
right now but it is not impossible for someone who is interested to add
a mp3 or mp4 encoder as long as they obey the licensing restrictions.
If you absolutely /must/ stream mp3, there's a hack to get ices0.3 to
transcode a vorbis stream into mp3. Email me if you want it. I'm doing
it on http://www.fallingforward.net