It looks like you have a great setup for your home theater system! As for amplifiers, both the Outlaw 7000x and OSD Audio Nero XA7180 are solid choices, and you're correct in that they have similar specs. The Outlaw has a slightly higher power output at 200 watts per channel compared to the Nero's 180 watts per channel, but both should be more than enough to power your speakers.
As for powering your ATMOS speakers, it's generally recommended to use a separate amplifier to ensure that they are receiving enough power and to avoid any strain on the main amplifier. You could consider using another Outlaw 7000x or Nero XA7180 to power the ATMOS speakers.
That being said, the Marantz Cinema 40 should be able to power your entire system, especially if you're not pushing the volume to extreme levels. However, if you're looking for more headroom and a potential improvement in sound quality, then a dedicated amplifier like the Outlaw or Nero would be a good investment.
In terms of alternatives, you could also consider amplifiers from Emotiva, NAD, and Anthem, which are all known for their high-quality amplifiers and offer options for multi-channel setups. Ultimately, the choice will come down to personal preference, budget, and the features you're looking for.
