Have you ever heard a dealer recommend a product they didn’t carry?
The marantz sound is nothing like the McIntosh sound. The marantz can’t compare to the better McIntosh integrateds, from today or from 20 years ago, nor can the marantz compare to the hegel’s, rogue, and I’m sure others.
If you like the marantz then keep it, but there are much better amps but you will have to pay a little more for used amps.
The marantz is low powered and any of the amps i mentioned above will have more real power/reserved power to drive your speakers. I had the flagship Hegel at the time, the H300 and it had 250 watts, the H360/390 have even more power. Besides the power, Hegel is a more neutral sounding amp. The dacs in any of these integrateds are a compromise compared to the vendors stand-alone dacs.
The rogue Cronus magnum is a powerful integrated amp with the kt120 tubes and it has a decent phono stage in it. Much warmer sound and more power than the marantz.
The McIntosh amps are warm sounding but have much more power and much better sound than your marantz. The new integrateds are 350 watts with many features inside, but is much more expensive. Look at a older MA6500 or MA6900