The goal of THX is to recreate the sound of a theater, with a lot of surrounds speakers, at home...
It's for 7.1 only, not for Atmos.
All the THX tricks we have in our processors have the same objective.

In a theater, surround are in height...

Having them at ear height is good for multichannel music.
Or Atmos, because there is another layer in ceiling.

But in 7.1 (and THX method), the goal is to have a diffuse surround sound, like in theater, with one layer only.

861v6 + HD621 / Cabasse Baltic