I'm not trying to be debbie downer, but here are some issues I see with what you're looking at doing:
1. Upfiring Atmos speakers are supposed to have a HRTF (Head Related Transfer Function) included in the xover (license fee to Dolby). Generic speakers and certainly DIYSG speakers will lack this
2. Upfiring Atmos generally needs to be carefully constructed of drivers that are only reproducing audio in region where they are "beaming" and are not reproducing sounds below that region of their response. This constrains sounds so you don't hear the direct sound and instead hear only what is reflected. Note that this is the exact opposite of what a good speaker (According to Toole etc) where it should have an even response over the entire listening area so very unlikely that a random speaker will possess those attributes
3. Upfiring Atmos generally have some absorption to kill any direct radiated sound to the listener, you would have to add that to the DIYSG speakers.
on top of all of that, I have heard theaters that have both the "Atmos" module, atmos speakers positioned onwall above the normal L/R and surrounds, as well as my theater has ceiling mounted (volt 6 in atmos format). I can tell you that I always think the modules sound terrible, don't care how expensive or compliant to the design. I find the effect to be weak and not convincing. The wall mounted setup is better, however you will need a REALLY tall room and to drop your side/rear surrounds really low to get enough separation of bed VS height channels.
When designing my theater using CAD, I figured out that getting a ceiling speaker with the proper dispersion pattern to cover your seating can be tough, Coax was the only viable solution for my ceiling mount atmos. I am 100% DIYSG and I love their products, but Atmos modules are possibly a poor (mis)use of their product.
TL;DR: Do ceiling speakers, potentially Coax, potentially sold by DIYSG