Perhaps it isn't very useful...
Oh man, you're lucky this isn't a musicians forum. You'd get flamed to hell for that remark :-D
Tubes are creme de la creme in the music world.
A good, expensive guitar amplifier has tubes, I'm about to buy a microphone preamp with tubes ... I could go on but instead I'll put it simple:
Tubes=good, expensive - solid state=bad, cheap
I'd definitely go for a Tube sound card if they were available in 24 bit/96kHz (i don't know much about them yet, maybe they are).
Tubes give an amplifier a warmer/more life-like sound and in recent years (with everything being retro) they have become far more popular than their solid state counterparts.
Even some
computermusicians insist on running their music out of the computer - through some form of tubed device (mixer/amp/whatever) - and then back into the computer instead of just exporting the audio directly to cd/wav/aiff/mp3/whatever.
And someone told me about an effect plugin (for audio apps) that simulates the sound of tubes (don't ask me how!), but I have been unable to dig that one up myself.
Btw.,
here is a topic on the topic :-D