Cassette Deck??

Tapes recorded on other decks sound excellent on Nak, at least as far as I can tell. Also, tapes that I recorded on my 682ZX sounded great in my Sony car deck.
But Nakamichi decks require attention.

Right. RTRs are history too, so are tube amps and vinyl. You might be able to get belt for your Sony deck on ebay; I got a quality belt for my twelve years old CEC cd player.

Elizabeth, your speakers are junk too. Throw them away and you won't regret it. Not to mention your turntables and cables. Amps are OK.

Some say Tandberg 3014, and 3014a, is the best there is. I never tried one. They are also very rare and expensive to buy and maintain.
Yes, my Spacedeck still sounds better than the copy made on my well aligned Nak 682ZX but not by too much. This Nak thing is really great especially with reference grade metal tape. I'll get to RTR later too. So for very critical listening - vinyl; not so critical - compilations on tape.

Let me tell you this. Recordings made on my Nak using Maxell Vertex tape, which is the best there is, directly from Acoustech phono using Purist cable fed by signal from the Spacedeck sound better in every respect except noise level than any CD. And RTR should be much better still. Decks are not obsolete at all; perhaps the people who think that way are. But yes, they require care and fine tuning and very good tapes. If majority of the population were not imbiciles we would be listening to only RTRs and some cassette decks now. No vinyl needed let alone cds.

Revox is very good and sounds somewhat different than Nakamichi. There are still places that service and repair them. Usually you can get one in good condition on ebay for about $500. I see no reason to use them instead of Nak.
Now, there are couple of Studer cassette decks that use better heads and all balanced in/out. They are rare and might be worth the attention. Expensive to buy and maintain.