Ok I made a slight change, so when streaming mp3 files on my server it should return audio/mpeg as content-type. It doesn't seem to change the behavior of anything anywhere, but at least I'm slightly more correct now. I was hoping this would fix my resume/partial content problem, but it doesn't seem to matter.

As far as the Content-Disposition line, you might want to try doing that also (if you don't see any drawbacks to it that I'm missing). That seems to be the fix that us Winamp folk were looking for. Similar to the way you generate the ext info in the m3u, I just generate on the fly a filename formated as <artist> - <title> and that's what shows up during stream/play in Winamp.