as far as number of speakers, past a certain number it’s more a room size and immersion by degrees issue. and then there is the reality that to get the best processor and the best feature set, that’s Trinnov, and their entry level is 16 channels (which can be expanded to 20 if need be).
i went from my Anthem AV60 with 7.1.4 to the Trinnov with 9.3.6 the quality difference of what i heard profound. same speakers, just a couple more of them. but night and day. the processor quality difference was game changing. and also the ability of the processor to ’re-map’ the locations of your speakers can make all the difference depending on your room challenges. i have a side window and side patio doors which effect where my 2 side speakers can be. no problem with the Trinnov, it will ’steer’ the perceived location with it’s set-up wizard.
so more speakers only help if the processor is up to the task of optimization.
and the Trinnov is really just a very large powerful computer, not any off the shelf chip set. and completely software based. so upgrades are downloaded and easy. little worry about the normal obsolescence as movie sound evolves.