I needed a sound card after being very dissapointed with the onboard sound on my laptop. After much searching on the internet the Xonar U3 and the Creative surround 5.1 seemed viable options, but I couldn't dedide which one so I bought both of them to try out.
I spent several days testing both sound cards doing a side by side comparison and in my oppinion the Xonar U3 is way ahead of the Creative surround 5.1 in sound quality.
I mainly use headphones and the Xonar U3's built in amp really does boost the output and goes much louder than you could possibly need, much louder than the Creative one.
The software with the Xonar installs easily and performs very well. In contrast, the software for the Creative takes forever to install and only really provides basic adjustments.
I compared the sound quality of both cards in games and music and much prefered the sound of the Xonar over the Creative.
The music and sound effects with the Xonar just seemed more lively and vivid somehow and the Dolby settings are impressive.
Both cards did a good job when it came to positional audio in games.
One thing that surprised me was how small the Xonar was compared to the Creative and yet seemed to out perform it easily.
If you need a USB sound card then don't waste your money like I did and get both, just get the Xonar U3.