You cannot use an Amp for Atmos height channels. The only height channels at this time are in the Arc, and simulated in the Beam Gen 2.
The request aside for a moment, I’m wondering you’re looking at Sonos for this situation? Why not get a standard AV receiver and wire your speakers for a 5.1.2 setup? Are you unable to wire speakers in the front or back of the room for some reason? Even if you wanted to be able stream with Sonos, or group with a other rooms, you can add a port to the setup.
This installation is in a tour bus, in the past we have mounted Playbars above the Salon TVs, and we choose to go with Sonos because of the simplicity. I have run out of the Playbars I've been hoarding.
I have no choice but to mount the Arc above the TV, albeit I can use an angle mount if needed, but will likely end-up turning the height speakers all the way down.
Hopefully its an easy firmware update in the future, and I can utilize the front installed speakers for height, in the meantime it'll just be similar to the 5.1 setup installed currently (Bose Lifestyle) but with the ability to control it with RTi.