I definitely agree with the suggestion of using a receiver with the anticipation of adding an amp at least for the front three channels in the future. Again, an amp is more a refining measure after you get others things up to par. And, it's really not about how "loud" the system is, but how...
That whole ported vs sealed argument has been repeated for decades. A lot has changed in that time with subwoofer design and options and it simply is no longer correct.
Over the last 2-3 years I switched from all ported subs to all sealed ones and will never look back. In the old days, ported...
Without going too deep into the weeds (which I can if you want) you might consider scaling back your system from 9.2.6 to 7.2.4. You could always wire it for 9.2.6 for future expansion if/when home Atmos capabilities expand in the future.
The fact is, home Atmos is somewhat limited, and it's...