Fun discussion. Good luck with all this. I have a few professional sound friends, one at the Ranch in Marin, another in post at the Presidio and one freelance but mostly involved in documentary filmmaking for TV. I love to listen to them discuss mic placement. I'm a physics guy, so I understand the science, but the art of what you do is special.
To your question about in-walls, I bought a pair of L-85s from Noble Fidelity a few years ago. The speakers are superior to most in-walls under $1000/pair, imho. I never expected them to match my previous setup from Dick Sequerra, but I needed something in the ceiling and frankly, they sound really great for things like organ music when paired with my old M&K sub. Problem with in-ceilings is that they're in the ceiling and with Covid, we're all working from home and every room is filled, so speakers in the ceiling are also speakers in the floor and that's a non-starter. Also, the reason I reference the organ is because in most places with an organ the sound is up, so an in-ceiling speaker makes sense. But for a Yo-yo Ma cello solo, the sound comes from the wrong place. The Noble Fidelity owner was great to work with and the product is quality. And they're in Reno. My kids actually prefer the Nobles to the On-wall Maggies I replaced them with, but I think that will change as I get the Maggies better dialed in.
I still have an M&K Volkswoofer, probably the same model you bought in 1980 - wasn't that demo that M&K did back then phenomenal? If you saw their roadshow, they'd setup the sat/sub combo and play a jazz recording with no noise. The initial cymbal crash would knock you out of the room because everyone was used to the sound of the needle on the record before the music started. I didn't like the satellites; they were too bright for me, but the sub was amazing used with various of Sequerra's setups. I've always lived in small houses (San Francisco Victorians), so I don't buy huge speakers, but I love the beauty.
G