First of all (and probably most importantly), the SQ2500 especially is made for accelerating applications that make use of Aureal's A3D 2.0 surround sound standard, as is mentioned under the specifications for digital audio acceleration. This allows for some very realistic and convincing 3D sound effects, using a fairly complicated process. Take Half-Life for example; when Gordon Freeman enters a room, the sound that his footsteps make start to echo around the hall. With A3D enabled, the SQ2500's wavetracing capability will start to track the sound as it travels across the room. When it hits against a particular obstacle, A3D will determine in real time what material the wall is made of, and will bounce or muffle the sound accordingly. What this translates into is that sound will be accurately stopped by concrete walls, given reverberation inside a steel chamber, leak through the bottoms of doors, etc. In other words, you won't be able to magically hear monsters inside a nearby enclosed room anymore, or listen to your opponent picking up weapons from an improbable distance.
Second, the SQ2500 comes with a nifty S/PDIF output jack, very useful if you feel like playing Unreal Tournament with your souped-up Dolby Digital home theater sound system. Good stuff, especially if you're like me and enjoy scaring the neighborhood kids with the massive bass rumble of exploding rockets.
Last of all, the SQ2500's SNR (signal to noise ratio) of 98 decibels is pretty respectable, and you can bet that you'll be getting high quality sound out of your speakers without a lot of that annoying background hiss. Altogether, all these statistics impressed me, especially the inclusion of an S/PDIF output on the card itself. Usually, most card manufacturers like to stiff you when it comes to extras, but Aureal makes the SQ2500 an even better value by throwing in this extra feature.