The VT1708 is a single-chip dedicated codec having built-in ADCs and DACs. As well as analog line ins and outs it has a "high-quality" headphone output, so it is capable of driving even low impedance phones directly. That chip (and the on-board "sound card" which is not really a "card") also supports S/PDIF in/out so a external ADC/DAC connected via S/PDIF is a easy possibility. That removes the analog circuits from "inside the box".
The DAC specification is decent at 100 dB S/N, but that's a decent spec for the chip (alone) and doesn't consider the fact that it's mounted on a mother board in close proximity to a lot of noisy digital circuitry, and is sharing power supplies with the same stuff. Low-level digital noise can
be a problem for such circuits.
A well designed outboard interface eliminates those potential problems, and usually
has better performance. However, having said that it comes down to what's good enough for your intended use. Some people wouldn't consider using anything less than top of the line Apogee or Lynx converters, for many, Mackie or Tascam is more than adequate, and for many musician's the real or perceived improvement of even those pieces of hardware is not necessary for their art.
You will find many opinions
on Gearslutz, and many absolute blanket declarations (i.e. X is ALWAYS better than Y or brand "B" is ALWAYS crap). Take them with a grain of salt.
The only way to tell if it's good enough for YOUR purposes is to try it. VT1708 PRODUCT FEATURES
Intel High Definition Audio Specification Rev.1.0 Compliant
Premium Audio Quality
* Supports 44.1K/48K/96K/192KHz DAC Independent Sample Rate
* All ADCs Support 48K/192KHz Independent Sample Rate
* Built in High Quality Headphone Amplifier
* Exceeds Microsoft PC2001 Requirements
Various Output Format
* 4 Stereo DACs Support 24-bit, 192KHz Samples
* DAC with 100dB S/N Ratio
* 2 Stereo ADCs Support 24-bit, 192KHz Samples
* ADC with 95dB S/N Ratio
* 8-Channels of DAC Support 16/20/24-bit PCM Format for 7.1 Audio Solution
* 16/20/24 bit S/PDIF TX Supports 24-bit, 44.1K/48K/96KHz Samples
* VT1708 supports S/PDIF out; VT1708A supports S/PDIF in and out
* High Quality Differential CD Input
* HPF In ADC Path for DC Removal
* Analog CD Input Path for Compatibility
Low Power Consumption
* Supports EAPD (External Amplifier Power Down)
* Power Management and Enhanced Power Saving Features
* Digital: 3.3V; Analog: 3.3V/5.0V
* Compatible with VIA VT1618 8-Channel AC'97 codec
* 48-Pin LQFP Package