Question has been asked before but need more info

Ok I have searched the archives including my own posts and I still dont understand the logic behind this concept.

If I have an all tube amplifier and a Solid state amp.
The amps job is simply to amplify the signal from the preamp.

Why would the I lose some of the tube signiture (holographic imaging 3/D etc) moving down the chain?

Why is it necessary to have a tube amp and a tube preamp to achieve this if the only job of the amp is simplly to amplify?

What makes a solid state amplifier warm or cold?

Confused in San Diego