I look at it several ways-
The Gold Reference Standard to me is the local Imaxhttp://www.thehenryford.org/imax/index.aspx
I believe the biggest real (not the re-branded Imax's at multiplexes) Imax in Michigan.
It uses real celluloid film and 6.1 audio- L-C-R-LS-RS and a center height channel (could be 7.1 with two off center height channels) plus subs. That's it. That's all that is needed to get good localization of sound and a 3D soundfield.
Yes, that venue is large so they can set it up for a large "sweet spot".
2 channel purists will tell you all you need is two speakers to achieve a 3-dimensional soundstage. While technically correct, the sweet spot will be very small- not good for home theaters seating more than two people.
So, the simple way to get some sound localization back it to add more speakers around you. How many channels and physical speakers are enough?
Again, the Imax and most commercial theaters should tell you. Why would you need more than the original commercial showings?
I could see some justification for 8.1-10.1 for a set of added sides and ceiling (Height) speakers, but that's the limit of plausibility IMO. That's assuming enough movies are released with enough discrete (no, artificially derived sound via funky processing doesn't count) activity in those added speakers to justify the added cost of decoders, amps, receivers, processors and speakers. Two rear speakers made sense to me for 6.1/7.1, but beyond that is getting comical.