Daniel R.

Problem 2: How to stop the sound looping?
Great the sound stopped, temporarily, only problem was when the SWF looped the sound started up again. The fix requires using a Loader and a call to unload() when you are done using it:

// create a loader and load the file
var loader:Loader = new Loader();
loader.load(new URLRequest("sound.swf"));

// later when you want to stop it
SoundMixer.stopAll();
loader.unload();

Problem 3: Security issues?
This works if you are requesting the SWF from your own server, but if you are using another site to store the sound files (say a CDN), you'll run into security sandbox issues. To get around this the remote site will need to have an appropriate crossdomain.xml file and you'll need to use a custom loader context:

// create the loader context
var loaderContext:LoaderContext = new LoaderContext();
loaderContext.securityDomain = SecurityDomain.currentDomain;
loaderContext.applicationDomain = ApplicationDomain.currentDomain;
loaderContext.checkPolicyFile = true;

// use it when loading the file
loader.load(new URLRequest("sound.swf"), loaderContext);

Other notes:
You should also setup a listener on loader.contentLoaderInfo to register when the SWF has loaded as unload() only works when the loader has completed, prior to that you need to use close().