[classicalman114]

If a device intended for computers uses a USB input rather than the machine's headphone jack (analog), is there truly  a difference in quality? I have a Logitech Z313 (a soundbar), and when I use it with a netbook my parents own, I am able to get a much louder signal out of it than if I were to use the headphone jack, which is considerably quiet on that computer. So I would say yes, but doesn't a computer's soundcard truly make the most difference in the quality of its audio signal, whether digital or analog? 

 

[Roseval]

The headphone out is a sound card (DAC + amp).
If you use the USB for audio you bypass the sound card completely and use the DAC + amp of the USB audio device.
A USB audio device is simply an outboard sound card

 

[gnarlsagan]

It depends on your soundcard. Mine sucks so I use a cheapo USB headphone out and it sounds better to me.

 

[Hifianddrumming]

I definitely feel USB out makes a difference, since you're bypassing all the noisy internals