Yeah I have one in my case. It's a graphic equalizer. You can adjust it by aura, be it Live, or Hall, or Concert, like any cheap equalizer, but you can also adjust the bands seperately. Although I haven't figured out how to do it yet.
It will make a crappy sound card sound great and a great sound card sound marginally better. It works well with my Live! and brought a SB128 up to Live standards in my opinion.
The external mic and headphone jack are a godsend for gaming. The only problem is the internal cable the plugs to the speaker output card is a little short. I have a full tower case and couldn't mount it in the top two slots and have it reach the second card slot from the top.
If you get one, get the DSP version that handles digital speakers. While I can't tell you the benefits as I run analog speakers, it's there if you ever decide to upgrade.
All in all it's not a bad item to have. It looks cool more than anything, but it will be getting replaced soon with an Audigy. Most usefulness in the Audigy than this thing.