It works on mine.
*I have installed twonky admin, I clicked on internet radio, I ticked shoutcast and saved it
*I created a playlist radio.m3u with 7 stations put it into the server
*In the admin page (click the "i" button) I see that it picked the 7 stations
*I go to xbox, music,playlists and I can see the radio playlist
*You can use each stream, play it as a "song"
make sure the format of the station is playable of xbox