Thanks again Spinaltap.
That snippet, along with many other critical observations regarding Atmos* that were encountered along the way, does nothing to convince that it is all worth while.
To summarise that and some of the others as to why Atmos disappoints:
(1) The Atmos soundtracks are often awful (i.e. poorly engineered and mastered)
(2) Good Atmos soundtracks may not even have any overhead effects (as though steered 3D objects cannot be used for 2D effects like a passing car/train/arrow)
(3) Even if the soundtrack has good Atmos effects, the processor is not good enough unless it can magically process Dolby Digital to make it sound better than Atmos
(4) The speakers are in the wrong place for the processor so you need one capable of fixing that
(5) And when the soundtrack, the processor and the speakers are all fixed, you are sitting in the wrong place...
Yes, I am being slightly disengenuous and selective.
But the last point just made me laugh. Atmos is designed for large cinema theatres with viewers all over the auditorium - so everyone is in the wrong place; the numerous effects channels are designed to fix exactly that problem in large spaces.
My only real experience to date with Atmos was "Gladiator II" in an Atmos-equipped cinema in Islington. It was OK but the front image from actor's voices was projected well into the auditorium away from the screen and seemed very unnatural. The surround/overhead effects were just like every other cinema.
* Using Atmos as short-hand for 3D object-based sound tracks and sound systems