Power Amplifier Longevity

I do like the sound of the Marantz and one of my intentions for picking up this unit is for the Atmos capability that I may implement down the road. 

Thank you all for your advice and information.  Much appreciated.

any thoughts on 'mcintosh' amps??

Buy a sugden class A and it can double as a space heater in winter! 😁 seriously though, there is nothing wrong with Marantz. I own the pm14s1 reference made in Japan and it is a terrific sounding integrated that I will never part with. The Sugden I have just sounds different, not necessarily better than my Marantz. 

Hello,
I can tell you from experience that having a really nice multichannel amp for home theater is awesome, but also very expensive. It sounds like you are trying to get two channel music an surround out of the same system. Marantz is my favorite Pre/pro. You have to realize that it is a processor. Even in pure mode it wants to color the sound in two channel. For now if you want higher end I would look at NAD class D for the center and surrounds. The processor can manipulate the sound to make the speakers blend together. Personally I would go with an Emotiva 5/4. Call them or look at the website and you will get it. You can have 5 high powered channels for the center and surrounds and use two of the slots for the 4 heights/ atmos. No risk because you can return it if you hate it. 

Now for the two channel. Now or later you would get a two channel preamp with home theater bypass. On the lower end you can go with an Emotiva USP - 1 ver 2 for $1100 retail and $750 eBay. Or on the high end Hegel for $4000. I have the Emotiva. I like that it lets you add the subs to your two channel setup and uses balanced input/ outputs if you want. 
Here is how it works: 
To listen to your system in stereo for music or TV you turn on your two channel preamp and stereo amp. High power great sound and pure as silk. When you want surround sound you turn on you Marantz Pre/pro and your multichannel amp which can be turned on using your 12v triggers along with your two channel setup if you choose. Push the HT bypass button on the two channel preamp and the Marantz controls the volume and sound of your two channel system. You can even program some of the two channel buttons on your Marantz remote so you do not need the 2 channel remote all the time. I love separates. It gives you control of your system. Later you can add a DAC to your two channel system for more better digital sound. That is a whole different thread. If your not into the music or two channel stick to my first response. Also everyone in this chat is correct about the caps on the older amps. Your speakers are very nice and I would be careful about older stuff. If you do by used please have it checked out by a professional before you hook it up. If the caps are bad or the gain or bias is set wrong you can do a lot of harm to your system. $50 can save you thousands.