Actually, the the Live! does have a noticeable amount of hissing. If I mute everything but wave and midi, which aren't playing, then I can hear a noticeable hiss. I know that some speakers and headphones have hiss anyway, but when I tried the same thing on my Santa Cruz card, there ware BARELY any hiss. I would turn the volume up all the way and barely hear any hiss with my headphones on. With my speakers, it's almost the same amount of hiss I'd hear if the sound card was muted.
As for the sound quality of portable CD players, some do have very clean outputs, usually the older models before all those extra memory, battery, and sound features were added.
I have to mention that vacuum tubes do provide better quality than transistors. I learned in my electronic circuits and signals and systems class that some of the reasons transistors are used is they last longer, are cheaper, smaller, and offer sound that is comparable to tubes. But to get the absolute best sound, a design using vacuum tubes is needed.