Old Amp vs. New Amp

Just to make sure, you are talking about amps specifically and not receivers, right?  I only ask because I see this become a misunderstanding too often!

That said, it all depends on what 90's models you are eyeing, the 90's had big changes as some manufacturers started production in China.  Generally speaking though, a good quality amplifier from the 90's could be a viable option today.  Just remember, an amp that has 20 years under its belt could develop issues.

Yep, Specifically power amps such as the older Krell's, Mark Levinson, PS Audio, Moon, etc.

I have a mid 90's Acurus A250 and a 2013 NAD 375BEE and I would consider them pretty much equal.

My feelings on technology in general is that technology can be great for some things, and not so good for others.  Technology generally makes things easier, faster and cheaper to manufacture.  But when it comes to sound quality, I'm not convinced.

Tubes for example.  When solid state came around, tubes largely disappeared but eventually people figured out that Solid State can't do what tubes do.

Also, IMO, the best recordings I have ever heard are from the 60's, 70's and 80's all done on analog gear.

And then there's vinyl...

The "Magazines" seem to indicate that the "New" version is better than the "Old" version, but I'm not sure if I'm buying it.

Of course magazines are reliant on advertising, and advertising is relying on selling you the "latest and greatest"

Okay, I have no direct experience with those brands you mentioned, but since they are top line brands, I think you'd be pretty safe with them.  My own experience with Nad is with the 326 and C356BEE.  The 356 is better at higher volumes, but when I compared it with a Parasound A21/P7 combo, the Parasounds kept their composure when the Nad was reaching its limits, and were only slightly better at lower volumes. This has made me curious about the Nad C375BEE.

Anyway, these brands are always suggesting that they've improved and have something better, but I agree that it's probably more marketing than anything else.  I am a believer in good cables, however!