Someone

USE="alsa mp3, mad, vorbis, wma" emerge -pv audacious-plugins

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N    ] media-libs/libmms-0.3  335 kB 
[ebuild   R   ] media-plugins/audacious-plugins-1.3.5  USE="alsa nls opengl wma* -aac -adplug -arts -chardet -esd -flac -jack -lirc -mad -modplug -musepack -oss -pulseaudio -sid -sndfile -timidity -tta -vorbis -wavpack" 0 kB 

Total: 2 packages (1 new, 1 reinstall), Size of downloads: 335 kB