The URL to the audio mixer class is...
http://jedi-sdl.cvs.sourceforge.net/...r.pas?view=log

Revision 1.4 is the latest version.

Within sdlaudiomixer.pas are several classes you can use...
TSDLSoundEffect - Handles just 1 sound effect
TSDLSoundEffectManager - Handles x sound effects
TSDLMusic - Handles just 1 music file
TSDLMusicManager - Handles x music files
TSDLAudioManager - Handle collections of both SoundEffects and Music files.

The SoundEffect and Music classes all support
Play
Stop
Pause
Resume
Rewind
as well as setting the Volume and Fading In and out.
You can also LoadFromFile. Though LoadFromStream exists as a method, these are not implemented yet.

A typical way of using TSDLSoundEffect or TSDLMusic on it's own would be ..
[pascal]var
MySoundEffect : TSDLSoundEffect;

begin
MySoundEffect : TSDLSoundEffect.Create('<path>\MyWavFile.wav');
MySoundEffect.Play;
end;[/pascal]

The Manager classes allows you to add several SoundEffect or Music classes and then refer to them by name or index after they have been added to their respective lists...

[pascal]MyAudoManager.SoundEffectNames['explosion'].Play;[/pascal]
or
[pascal]MyAudoManager.TrackNames['background'].Play;[/pascal]

Note in order to compile and use this you will also need the other sdl related files that these classes are built from. Namely
sdl_mixer - http://jedi-sdl.cvs.sourceforge.net/...r.pas?view=log

sdl - http://jedi-sdl.cvs.sourceforge.net/...l.pas?view=log

smpeg - http://jedi-sdl.cvs.sourceforge.net/...g.pas?view=log