Valve/Tube Amps Answered

Hi,
I am currently designing a stereo/mp3 amp for my education and I was wondering...

Is it possible to incorporate a Valve/tube into a conventional stereo circuit?
(like a standard valve amp but smaller and without the Equalization effects)
I suppose the Valve/tube watts would have to match the speakers, but is this possible or would I have to use a circuit from a guitar amp that is already paired with a valve/tube amp system?!

Much appreciated.
-Rob