I think the that in the end it’s dependent on the room. In my 16x12x8 apartment I found 5.1 worked better than 7.1. I literally had as perfect a 360 degree soundstage as I could imagine. In my 21x13x8-12vaulted I find that 9.2 with wide speakers and a Buttkicker are about as good as I’m going to get. In the second case the longer room greatly benefits from wide speakers because they fill that gap between the mains and the surrounds caused by room length.
IMO a close to square room (not really square) is perfect for creating a 360 degree soundstage in the sweet spot or for all seats if the walls are far enough away. However, the longer the room and the more rows of seats the more having wide or multiple surround speakers benefit the presentation.
I don’t think HT audio will benefit from many more channels unless we break free from having the video projected only up front. If a wider range of video angles are present then I could see an advantage to adding more audio channels so better support the 180 or say 360 degree on screen action.
