1) Add a reference to SfxrSynth to your project.
2) Make a cool sound effect in as3sfxr
3) Hit Control + C to copy the settings to your clipboard.
3) Create a Synthesizer object. Paste the settings as a parameter for the CreateSound method.
Synthesizer s = new Synthesizer();
SoundEffect se = s.CreateSound("1,,0.2117,,0.4824,0.31,,0.4335,,,,,,,,0.7391,,,1,,,,,0.5");
For an example, you should take a look at the SfxrSynthTest project that's included if you check out the code.