Re the Marantz receivers -- I and probably a certain number of others on this site used to sell, own or repair them and other contemporary units. Some of us still own one or more.
At the time they were among the best of mass-market gear. Sonically they can be quite agreeable but as an owner and ex-salesman I feel they honestly don't stack up against the modern units you've had suggested to you in this thread. (It hardly bears pointing out that the modern high end units are more expensive than used gear 30 or 40 years old.)
Although Yammie receivers contemporary with those Marantzes sounded almost as good, mass market electronics took a turn for the worse in the 1980s and have continued that way. I have not heard your Yamaha but I would not expect it to sound as musical as the best-built 2-channel Yamahas from the 70s. That means the antique Marantzes may sound nicer than the Yamaha receiver you have today, but not, I think, so much nicer that you could refer to them as an upgrade. More what is known as a sidegrade, and sidegrades are expensive detours on the way to audio bliss.
And then there is the question of maintaining gear that is 30 or 40 years old.
At the time they were among the best of mass-market gear. Sonically they can be quite agreeable but as an owner and ex-salesman I feel they honestly don't stack up against the modern units you've had suggested to you in this thread. (It hardly bears pointing out that the modern high end units are more expensive than used gear 30 or 40 years old.)
Although Yammie receivers contemporary with those Marantzes sounded almost as good, mass market electronics took a turn for the worse in the 1980s and have continued that way. I have not heard your Yamaha but I would not expect it to sound as musical as the best-built 2-channel Yamahas from the 70s. That means the antique Marantzes may sound nicer than the Yamaha receiver you have today, but not, I think, so much nicer that you could refer to them as an upgrade. More what is known as a sidegrade, and sidegrades are expensive detours on the way to audio bliss.
And then there is the question of maintaining gear that is 30 or 40 years old.