thanks for the reply.. that's a good point about amount of inputs, if I was using pre-outs that helps out. I hadn't thought of that.
Technically I can tell the receiver to do anything regardless of where the speakers are, yes. It sounds like on wall is preferred to in ceiling, when doing auro/atmos "hybrid." Pretty much, I've seen a lot of chatter about auro and am curious to try it. So I'm going to put some height/on wall speakers in eventually. And if I end up preferring them to the in-ceiling, it'd just be nice to be able to now and then switch to the (obsolete) ceiling speakers easily to A/B compare, or just for funsies.
(I think I enjoy tinkering and changing things more than using the system, is the problem!)