Audioengine recently released a premium 24-bit DAC (digital to analog converter) that lets you bypass your Mac headphone jack and send the audio through a USB port. The result is an audible and sometimes dramatic improvement in music quality. The D3 is US$189.00, a very reasonable price as high-quality DACs go.
The D3 DAC allows you to stream bit-perfect native 24-bit/96 KHz HD audio. Installation is simple. The hardware unit looks like a small thumbdrive, and its aluminum housing is a perfect match for a Mac laptop. There are no drivers to install; you simply select your sound system in the preference pane and the DAC is recognized as an output device. Plug in some high-quality headphones or powered speakers and you are ready to go. There are two small LEDs on the D3 -- one shows power from the USB bus; the other shows the presence of a data stream above 48K. For listening, volume is controlled from the volume control on your Mac.
Because the D3 essentially replaces the Apple sound system, anything with audio will come through the D3, such as a game, a movie or any sound file Apple supports.