Sound enhancers are nothing new. Windows Media Player has SRS TruBass and WOW, which enhance bass and expand the sound field, built right in. iTunes and many MP3 players (with the noticeable exception of the iPod series) also have enhancers. However, AstoundSound Expander ($40, 30-day free trial) is rather unique in the consumer field in its ability to create a 3D sound field with virtually no fuss.
There's not a whole lot to using AstoundSound Expander. You install it and it then sits in the system tray doing its background processing on all audio passing through any particular output. If you have multiple audio output devices, you may select which one the effect works on. There are three buttons that will optimize the effect for movies, music, and games, as well as a slider that varies the intensity of the effect, and a pre-amp slider that will add gain to the input signal. There's also a recycle button to re-enable the effect should it get locked out of the audio chain, which happened once to me with the VLC player when I left AstoundSound Expander off for a while. The effect also crashed once and required a reboot of the system for sound to return.
I was skeptical before I installed AstoundSound Expander. However, it really does create an illusion of depth that I'd not heard before outside of the $30 SRS HD Audio Lab and high-end audio workstation plugins (which will also available from GenAudio soon). SRS WOW and the iTunes sound enhancer tend to broaden the sound field laterally, and so does AstoundSound Expander, but with ASE, certain sounds appear nearer to you than others. As with all sound field effects, the results vary by the material, and it helps to be dead center between the speakers (it won't work with mono systems). I enjoyed ASE more with movies than with music, though it's effective with both depending on the intensity. My only wish is that it would allow you to pump up the bass a bit.
AstoundSound Expander performs as advertised and works on the output of any media player though you may suffer the occasional crash. It's simpler to use than SRS HD Audio Lab, if not as tweakable, although it lacks the latter's bass enhancement. Whether AstoundSound Expander is a big enough thrill or improvement on built-in enhancers to plop down a fair amount of cash for it is up to you, but it's most definitely worth checking out the free trial.