Well, if you've been researching for months, I probably can't be of much use to you
But the seat-back thing caught my eye. We sit on a (lovely, Thomasville) sofa that my wife has always really liked. It's comfy, and I would never sacrifice the ability to sit directly next to her (i.e. if we got theater seats, we'd have a loveseat in the middle or something).
I'm rambling, but my point was going to be that the sofa has a pretty high back. My perception is that it meaningfully compromises the effectiveness of the surround sound. Admittedly, my surround speakers are a little behind (rather than a little in front of) the seating position. And the sofa could well be the reason why I didn't get all tingly by going from 5.1 to 7.1.
Theater seating and speakers both cost a lot of money. Speaker placement matters, and so does ear placement.
