For starters, one of the main selling points of the U7 is the built in headphone amplifier. Asus recognizes that most sound cards and onboard audio solutions do not carry a headphone amplifier, and that most consumers aren't willing to buy a separate headphone amplifier. The advantage of a good headphone amplifier can be very broad, and its purpose is not only to make the headphones louder, but also to dramatically increase the sound quality of the signal, as a system without a headphone amplifier may provide enough power to drive headphones to be loud, but not in a controlled manner.
The DACs (Digital to Analogue converters) in the device are Cirrus Logic CS4398's, which are renowned for crystal clear conversion.
Beyond this, Asus also mentions that the device has a signal-to-noise ratio (SNR) of a staggering 114 dB, and it features Dolby Home Theater V4 with a coaxial S/PDIF output. The unit also has a 3.5 mm headphone out jack, as well as a 3.5 mm microphone jack.
The Xonar U7 is also fully powered by the USB only, so there is no need for any extra adapters.
So far there is no word on pricing or availability.