[PCMbinaryaudio]

I still have not used an audio interface until today.
 
Whenever I've listened to audio CDs in the DVD-ROM drive I've always had interference from the motor of the DVD-ROM drive and analog noise.
The headphone output is on the motherboard using Realtek AC'97 Audio.
Even when just using Windows Media Player 11 the audio was not very good.
 
Wow!  From a first time user I'm amazed how much better the audio it without any analog circuitry in the motherboard!
 

I've had a Zoom H4n recorder for 6 months and only used it to record things on location.
 
The H4n also functions as a USB audio interface @ 44.1 or 48kHz only.
and can be used as a 2-channel interface to record you can also use it as a headphone amp. (It only has 1/8" jack)
http://www.zoom.co.jp/english/products/h4n/
 
using Windows Media Player 11 I turned the volume to maxium, and also in the H4n driver sound level control I turned the audio all the way up on the H4n itself and there is no hiss on a digital recording!
I recorded a live concert in November and only today am I hearing how great the bass guitar direct out ISO is! You can hear fingerpicks and deep bass.
 
I used a PC (Windows XP Professional SP3) plug & play USB 2.0.
When you turn on the Zoom H4n it asks what sampling rate you will use to connect (44.1/48) and then it works. 
Using Windows Media Player 11 I tried playing a 48kHz file after I already set it to 44.1 and it tried to do playback at the wrong rate and there was very nasty loud artifacts which means you must unplug and replug & choose the other sampling rate to play the other files.
 
I could even play crappy General MIDI files (using Windows Media Player 11) via the SW Synth on the motherboard but had to unplug & plug in the Zoom H4n and choose 48kHz sampling rate (which apparently is the raw sampling rate the Realtek AC'97 Audio uses) and it was super quiet when I paused the playback.
 
So while it doesn't work as a USB 2.0 audio interface for 88.2/96/176/192 it does pretty well for the 98 percent of digital music I have at 48kHz and below for headphone listening.
Zoom H4n street cost is  $299.00 
 
for comparison the E-MU 0404 USB 2.0 - Audio/MIDI Interface (White)  street cost is $197.
http://www.emu.com/products/product.asp?category=610&subcategory=611&product=15185
[24-bit/192kHz analog-to-digital and digital-to-analog converters]
and it also has SPDIF IN/OUT on
coaxial (transformer coupled)
optical
    - AES/EBU or S/PDIF format (software selectable)
If I didn't need this little recorder for work I would go with the highly recommended E-MU 0404 USB 2.0 for $200. as an external DAC is really is a huge difference in audio quality.
 
I'm now a believer.
I may have to remix the concert I mixed using the Realtek AC'97 Audio's analog headphone out on the motherboard...