Amp improvement since 1994?

Interesting question as designing and building a circuit to amplify an audio signal is a fairly simple task. While there have been improvements in parts available as well as improvements in getting amps to react with different speaker designs, the basic principles haven't changed.

Many audiophiles prefer amps designed and built in the 50s and 60s so we know it has been done well for years. I'm interested to see what others have to say.

digital amps widely used in audiophile applicaions.

I would say the transparency has took a step up with modern amps from 2000 to 2014, real old amps to me sound like very old out dated speakers compaired to any speaker from 1992 to present.

It depends on what you mean by "real" improvement. Probably nothing that can be measured.
I do agree that the trend seems to be towards transparency/resolution and away from musicality, but I'm not sure that is a good thing. My old tube amp beats most of the modern amps out there now, IMHO.

As to your last question, where the gains have been, I would suggest mostly in the price tag.