Via ASUS: "Hot on the heels on the success of the Xonar D2 audio card, ASUS, worldwide leader in motherboard and graphics cards, now offers users even more audio choices by introducing the first PCI-E interface audio card Xonar D2X; and the stylish USB interface audio device Xonar U1. Providing solutions for the gaming audio issue found in Windows Vista by utilizing DS3D GX, and Acoustic Echo Cancellation (AEC) for best voice communication quality, the Xonar D2X will undoubtedly provide the best gaming experience ever. The Xonar U1 on the other hand will feature eye-catching industrial design, a convenient user interface and total compatibility with both PCs and notebooks.
ASUS Xonar D2X -Solution to Windows Vista Gaming Audio Problems

With the introduction of Windows Vista, the whole audio architecture landscaped has been changed. This has resulted in teething problems for gamers – with the possibility of losing all surround sound or hardware accelerated Direct3D and EAX while gaming in the Windows Vista environment. To circumvent this problem, the ASUS Xonar family of audio cards utilizes an ASUS exclusive technology – the new DS3D GX extension in the Xonar D2X driver; to provide full support for surround sound and hardware accelerated features by translating DirectX to the DS3D GX. While other solutions like OpenAL requires special installation and game support, DS3D GX doesn’t. Gamers can enjoy DirectX gaming with hardware enhanced surround sound and EAX effects automatically and immediately after installation.

The Xonar U1 is an external USB audio device that improves the laptop or PC’s underachieving audio by first eliminating electromagnetic interference (EMI) and noisy DC circuits inside the PC chassis. It then utilizes the high quality DAC (digital to analog convertor) to bring about crisp, clear music or gaming audio in the original flavor that was meant to be heard. The Xonar U1 provides a huge boost to PC gamers by supporting EAX and DirectSound HW acceleration for best gaming experience in Windows VISTA and XP."

Where do you get your audio source from?

Discrete sound card! (Audigy, Xonar, etc)

Integrated (Realtek, etc)

External USB soundcard (SteelSeries, Sennheiser, etc)

Other?

Source @ ASUS