I'm still not sure what a DAC actually does. It get's the audio through the USB port, but isn't a USB sound card?
A sound card will also let you record (ADC).
(I feel sad, just a couple of days ago I looked into an old pc case and saw my Aureal Vortex 2 sound card. Damn it was good. Real time reverb and occlusion calculation using 3D wave tracing rocked. Creative bought out and shut down the company before they could finish the win2000/xp drivers)
You can think of a DAC sort of as an external sound card (which supports input via USB and typically other digital cable types), but really despite DACs and sound cards having some overlapping features, there are some differences. A sound card usually features some recording / input capability as mentioned above, a DAC does not. A sound card usually includes some kind of digital audio processing chip (for equalization, hardware mixing, etc.), a DAC does not - its sole job is to take a single digital audio signal and output it as an analog one. Sound cards are internal, whereas DACs are external and often have a variety if inputs to select from, as well as various outputs sometimes too.
The most important difference is that DACs generally have sound quality consistently far superior to even the best sound cards (for various reasons). It's also nice to have your sound system components mostly external to your computer, especially if you use the same sound system from multiple computers. I use my DAC from my desktop computer's TOSLINK digital optical out (so I can use my sound cards equalizer and other digital processing features) and simultaneously connected to my laptop via USB - then I can switch between them with a simple flip of a switch on my DAC.
Another advantage of an "external sound card" like this is you can get a combo DAC/amp unit (this is what I have). A DAC alone is usually meant be plugged into an amplifier rather than itself driving a headphone. The downside is that getting a good DAC+amp unit would probably cost about the same as your headphones alone.
But anyway I hope this makes sense, regarding your DAC questions.
The term DAC is a bit unspecific in this case though, since all sound cards, all graphics cards with vga ports and most graphics cards with dvi ports contain DACs. They aren't limited to audio. The usb devices we are talking about here should really be called something like external audio DAC.
Although I'm sure that won't help the marketing.
Okay, I just settled on a normal switching box from Amazon. It has good reviews, and a few forum posts about it on the internet. It does use phono inputs, so I had to buy the appropriate cables for it.
I'll post again, once I have it and try it out. Thank you all for your comments.
