Maybe I misrepresented my suggestion.
I'm hinging on the relative simplicity and the fact it's built in, purely for personal use - not concerned with making it powerful radio software, haha. The only thing that needs to happen to broadcast over the internet is a port forward.
The way to go about sharing your currently playing music at the moment is to go into Preferences > Streaming and then hit the 'Start Server' button, then go into Preferences > Streaming > Stream Source and hit the 'Connect' button. Then of course have someone directly connect by passing them your IP/domain.
I'm just suggesting being able to click those buttons programmatically somehow. For example, another program could execute winamp with some command line switch, and that program would also handle giving the link to whomever is requesting to join in (ie. some IM software plugin that is also showing that you're listening to music). Thinking about it, it probably would be more sensible to just have the one switch that starts the server then connects the source in one go, to avoid trying to connect the source when no server is running - was mainly thinking of separate Icecast/Shoutcast servers (which can obviously be started programmatically anyway).
Forgive my ignorance if I'm missing something simple though! It currently works with just "auto start server" and "auto connect stream source", but to have it running when maybe 80% of the time no one is interested in listening in feels a little unnecessary.