I'm using the foo_vis_shpeck component for Foobar2000 to emulate Winamp, and it will works. The only thing is that STO doesn't detect it if you arn't playing anything when STO starts up. You have to hit "play" in Foobar first, then STO will detect it.
No clue with "real" Winamp. (Haven't used it since AOL bought out Nullsoft and fired the original team)