Description:

xmmsao is (at this point) a rudimentary xmms output plugin that uses the
ao audio output library. The great benefit of this is that, whether your
sound system is OSS, ALSA, ESD, or aRts, the sound will work. You can
(pressing stop in-between) switch among those, and the plugin will adapt.
It is ideal for users who switch regularly between desktop environments
or for admins who are tired of fielding "why doesn't xmms-esd work in KDE?"
questions.

At this point, xmmsao only outputs audio; it does not aupport any sort of
effect plugins or even mixing. If you absolutely require support for these,
then selecting another xmms output plugin is recommended.