Hi
IMHO, Marantz AVRs are built to last provided you use them appropriately within their recommended usage and specs.
The SR5006 is quite an old model, there has been changes after that (5007, 5008, 5009 and 5010). The 5008 has been built like a tank to last and i have not faced any issues.
If you are looking at Denon (Same company D & M Holdings make the Marantz AVR), you will find a difference in performance signature as normal components are used. It is only the higher models (3000/4000 series) which sound good enough.
Pioneer 800 series is good but LX series is better from a performance and durability standpoint which i seen and heard at the What Hi Fi Show.
Yamaha was good in the past and i did own AVRs of the same brand a good number of years and kept changing models.....now the quality has somehow gone down and so has performance.....
Remember any AVR can give a performance and claim it is the best....you as a user and owner should be sharp enough to notice the difference and make up your mind on what you expect. Hence audition before purchasing any other brand than the one you have used.
For me Dolby Atmos is not a priority as there is hardly any much difference to a 7.1 setup. As most of us know, its a marketing gimmick where all want to capitalise. Also not much content is out there ..the most imp thing is that you need extra speakers or specially designed dolby atmos speakers to enjoy.....
Wifi or Bluetooth feature is another strategy to sell AVRs..honestly if there are too many antennaes in the area....signals get mixed up and streaming or capabilities faces issues..
Anyways, all the best.....hope you find something that fits your budget and expectations. There are some good AVRs on sale in Hi Fi Ads and For Sale by Owner....all the best.