I think one of the most difficult things about the audio/video hobby is recognizing when you've reached the point of diminishing returns. I am very old-school about my audio setup- you don't need all the latest bells and whistles to run a turntable through a quality amp and some kick-a** speakers- and I've heard systems that cost 5-6x more than mine with no significant difference in sound quality, at least in a home audio setting. Perhaps if those systems were pushing out sound in an auditorium there would be a difference, but it's somewhat similar to having a 900hp Ferrari, which you can never use to its potential in the real world.
Can't agree more on the diminishing returns in the field emissions (true audio quality) game, especially with room gain considered. I went down a quest to score a 99 on FE (now "sq") in usaci (automotive) back in the early 2000's and grew out of that phase of life quickly. It's true that with decent "reference series" gear, 2.1, you can achieve a nice flat curve in a or c weighting as long as you can control room gain and stay within q. This is a great starting (and ending) point for listening to music meant to sound as if the stage is in front of you and honestly to most ears sounds better while listening to music than 99.999 percent of home theater systems will. I don't listen to music on my theater system speakers, I have a basic pair of older JBL floor speakers that do the trick without any special decoding. They aren't a flat curve, they just sound "right", up until the room echoes back.
As far as home theater, low spl spacial reconstruction has been a sticking thing for me since I was little and my father taught me how to decode quadraphonics on diy equipment. There's a track I use for reference that features a single person walking around a hot room playing a guiro. If sitting in the center of the array, you should hear the instrumentalist moving around you as if you were in the middle of his actual room. This would make for a very boring concert, but if applied right and balanced with the right low frequency effect engine (not a musical sounding subwoofer, LFE is too boomy for even the most enthusiastic metalhead) it makes for a great addition to an immersive movie scene, or in the case of modern video games can get you significantly deeper into a driving or flight simulation type game.
When we moved in and I remodeled the first floor of the house I wired it for 5.1, my room isn't perfect for a screen to be centered due to a door, so I have a hinge system that moves the TV when I want such an experience. It was easy to move to 5.2 but I didn't find it to change the stage enough to justify the space, so I traded the second LFE sub to someone for a very near match to my Forward L and R channel full range speakers, moved my couch back and dropped a set of wires in the back of the room to move the smaller rear channels further back. Having speakers that can run below 120hz (my small rears recommend a steep crossover above 120) as the new wide right and wide left really opened up the ability to hear larger things around me, not just localization of voices. The really "loud" scenes with wideband noise like jet engines circling aren't much better, but a car engine idling next to you is much more believable. As far as the gentleman with the guiro, it wasn't recorded for 7.1 so I cannot report a success worth cutting my walls open or popping baseboards(return effectively diminished, and I probably won't be going to 9.1, but still would go watch and listen at a friend's house lol).