For subjective listening, I compare the Xtreme Sound 7.1 DDL to the Sound Blaster X-Fi. The audition was set up using two different PCs connected to a Kenwood VR-606 digital receiver with Kenwood speakers and subwoofer. The volume from each sound card was normalized to the same level, and coax and optical digital cables were used for the X-Fi and Xtreme Sound 7.1 respectively.
When listening to the same music, I found the bass on the X-Fi a bit cleaner and articulated than the Xtreme Sound. The bass on the Xtreme sounded a bit muddier as if the source audio was being compressed.
In 5.1 channel output, the Xtreme Sound 7.1 generally produces a wide sound stage which is a result of being a bit heavy on the front left and right speakers. This effect varied depending on the source media, but generally noticeable when compared to the Creative Labs X-Fi. In contrast, the X-Fi did a more consistent job at anchoring music using the center channel and while using the front left and right speakers for ambience. I can’t say which is better as both cards sound decent even though their presentation is slightly different from each other.
In the case of DVD movies, the Xtreme Sound 7.1 delivered dialog mainly through the left and right speakers, whereas the X-Fi uses the center channel more.
In a home theater setting, I prefer having the action (dialog or otherwise) produced on the center channel since it coincides with the visuals in the center of your vision, in this respect I find the X-Fi better.
The Xear3D option on the Diamond Xtreme Sound is excellent as it helps improve the audio quite drastically. In the case of DVD movies, the effects of shattering glass sounded sharper and more lethal, and music more defined and carried more depth.
Unfortunately, the Xear3D option has no other adjustment from turning it on or off. You can use the same feature to virtually shift the speakers around which may be useful in fine tuning your setup.