I have had this sound card for a couple months now, and have found that the quality of sound is very good for the price.
Labelled as a 'Gaming' soundcard, this unit also boasts 118db Clarity SNR, EMI shielding, 3 headphone gain settings (up to 600ohm), Dolby Home Theater V4,, and an analog sample rate of up to 192KHz @ 24bit. The card can also be hooked up to 7.1 PC audio via 5x3.5mm, and has S/PDIF or Toslink output.
For the audiophile, you will appreciate the higher gain settings that allow you to drive pretty much any headphone you can throw at it, and the higher sample rate options. Noise levels are very low, and I appreciate the Dolby settings which allow me to customize the output to suit my tastes, or leave everything off for a clean and unmodified sound. This sound card does require pci express slot and a 6 pin PCI express power supply connector (it comes with a dual molex to PCI Express Adapter if needed), presumably to bypass noise generated using the power from the motherboard. The extension component (which also doubles as a noise-cancelling microphone and volume control) is a nice touch which also has headphone and microphone output, and allows for placement and swapping of the headphone jack just about anywhere without rigging things up at the sound card. The outputs are also lighted green and red on both the sound card and the extension to make it easy to identify which is a microphone output (red) and which is for headphones (green).
Drivers should be installed from the Asus website, as there are updates that improve compatibility with some gaming titles. However, I have found that updates from Asus on drivers are few and far between thus far, and I wish they would address a nagging issue where gain settings for headphones are not saved upon reboot (perhaps to prevent the user from destroying cheap headphones by using them with accidental high gain settings). I have also used this sound card with Windows 8, and came across a problem where the operating system would not detect the card. I assume that Asus is still working on this issue, but if you plan on using this card with Windows 8, I would look into whether this has been address yet or not before purchasing.
There are a number of additional software features. There is Xear audio engine is used to enhance gaming sound, magic voice to enhance voices, and flexxbass for more bass response, and Dolby Home Theater V4. Of all of these features, I have found the Dolby enhancement to add a nice touch to the sound quality, bringing out more of the mids and highs in music, and allows for more detailed customization of the sound levels. The dolby music setting by default tones down the mid's which I did not like, so I opted to select a customize option in the Dolby configuration so I could set my own levels using the equalizer.
Overall, this is a great card, with sufficient enough options to satisfy the average audiophile. A decent external DAC may or may not produce better sound (I have yet to test the difference as i'm still a new audiophile, but will update when I test with a future Schiit Bifrost for comparison), but for someone that wants the ability to both improve sound for applications/games, and sound for strictly audio listening, this satisfies both needs and should be on the shortlist of great desktop audio solution to consider.
I am currently using this sound card with a set of Sennheiser HD 650's.
