Modern Class D is different. Class AB hasn’t changed much

I recently picked up an Onkyo M-5030 power amp and a Nikko Beta II preamp. They are from the late 70’s/early 80’s and sound pretty amazing considering the age. Both devices need some love but as is in survivor condition they both sound fantastic.

the most basic answer is they are the same, except the newer dac technology as you have stated. That is not 100% true but i think it answers the question.

you probably have to consider each case by case, if you are getting a good price, is the condition good, etc.

With respect to the power amplifier component of integrated amps, Class D has vastly improved over the last 20 years. So a 20 year old class D may be obsolete whereas so modern class D is arguably the state of the art for power amplification. Class A & AB has not changed appreciably over that timeframe. The best Class D today competes with Class AB in sound quality and can outperform driving difficult loads.

With respect to the preamp section, incorporating tube buffers in the preamp section has become more common and can introduce a very pleasing sonic character vs solid state preamplifier sections. Whether that’s an improvement is a matter of taste. But it’s more accessible now with broader availability in lower priced gear.

Likewise all tube integrated amplifiers are more broadly available at lower prices for those who enjoy tubes.

My system uses a Bottlehead preamp and phono preamp and a Hypex power amp and that combo sounds fantastic. It’s not an integrated amp, but the point is the combination of tube preamp and class D power pairs extremely well in my experience.

The classic linear amplifiers are well studied and things have improved over time as semiconductor technology has. If this improvement translates in better sound is debatable, I’d say that better passive components and power supplies improve sound much more. Class D is another story, it’s a rapidly evolving technology.