You can control any loaded movie with the path that it was loaded with. I prefer to load into a movieclip as it gives you a few more presentation options, but if your loading a movie into a level, to control that movies timeline, use the path you used to load it.......
You could also use the stopAllSounds method...
If your using Flash MX or higher, there is a built in object for dealing with sound. Loading sound into a .swf that you load into another movie is Flash 5 methodology. The sound object can dynamically load external mp3 files at runtime. I have an mp3 player demo on my site that loads external MP3 files dynamically into the sound object.
mySound = new Sound();
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