I'd stick with Denon - they are still a fairly premier brand. Onkyo has had some issues with their HDMI chipsets in the past, and basically replaced the low-end Pioneer line after they acquired Pioneer's home theater business.
Here is a simple rule of thumb regarding Atmos and receivers:
* A 7.1 or 7.2 receiver can only provide a 5.1.2 configuration (2 height channels)
* A 9.1 or 9.2 receiver can provide either 5.1.2, 5.1.4, or 7.1.2
* An 11.2 receiver can provide all of the above, up to 7.1.4
* The just-announced...