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.
However, Grunt they say an un-equilateral room is best suited for HT and sound waves. So, your second room seems better un equal odd sizes as oppose to a 10x10x10.
Like if the sound wave hita the side way at 45 it will bounce off at 45 to the next to the next to the next always in the same spot. No real disspertion
