The biggest hurdle with Atmos (aside from the addiction of adding more and more speakers) is the receiver/amp situation.

7.x (non-Atmos) receivers are ubiquitous ("x" can be anywhere from 1 sub to 4, but that doesn't matter here).

But if they have Atmos onboard, then can switch between:

7.x vs 5.x.2

(the ceiling ".2" speakers need to be amplified, so they eat up two of the 7 channels).

So a 7-channel Atmos receiver is really your minimum.

If you want 5.x.4, you need a 9-channel amp. Starting to get more expensive.

But the full Atmos spec supports 7.x.y ("y" = in theory I think you can go insane to like 30 ceiling speakers).

If you want 7.x.4, that's 11 total channels. Only a few really high-end receivers provide that many amped channels. Megabucks.

BUT the clever workaround is that there are 7- and 9-channel receivers that offer you the line-level (not amplified) audio out for the missing channels, you just have to pipe that to a separate amp.

And in my case, my separate amp is the GOOD AMP. So even though my receiver can amplify 9 channels(?), I'm only using 6 of them and instead I have my good amp doing the most important work:

Proceed AMP5: L, R, C, side L, side R

Receiver: rear L, rear R, top front L, top front R, top rear L, top rear R