All other things being equal, streaming your digital signal from your computer to your system will sound the same as if it were played by a CD transport. The biggest factor is the sound of the receiving unit (such as a Squeezebox) or the DAC to which the receiver is attached.

The analog outs of the Squeezebox sound fine, not great, but good - the equivalent of a similarly priced CD player. I have not personally heard the others so I cannot comment.

You may want to look at the computer audio threads below as they may answer some of your questions.

The Apple Airport does a great job of getting the music from computer to stereo (if you already have a wireless network). I use it for streaming uncompressed files from iTunes, but I also feed it into a separate DAC and bypass the built in one on the Airport. It sounds much better, although not nearly as good as my CD player (which is at least twice the cost). In any case, for what I want for (quick and dirty way to make music happen while cooking, taking care of my kid or for parties) it's great. I use the Channel Islands Audio VDA-1 by the way. Very good for the price ($450)- unfortunately discontinued. The new VDA-2 is $699 so it gets pricey. Look on Audiogon maybe? Good luck!