I think I have the receiver option figured out after a ton of reading. At least the "how" part.
Since we're on a new page, here's the layout diagram for reference.
Behind the cabinet I would add a wall plate with banana jacks. I would drill 1 or 2 holes through the bottom 2x4 into the joist space. Then I'll add similar plates (less connections) behind the couch on the left, and back/right corner behind the primary couch.
The runs themselves would be from the receiver to the plate, then from the plate down, to the left about 10ft to where I have joist access in the basement. Then 15ft towards the bottom, along the joist to the bottom right corner area where I already have a defunct phone drop with a blank plate over it already. That would allow for 2 back speakers and one right surround.
The run to the plate behind the left couch would be about half that run.
Later on if I want to add more, I can run additional cables to additional jacks.
Now, I've figured the longest run (plate to plate distance only) to be about 43ft. Add another 10ft onto that for total longest run (back left speaker), and that's a hefty bit of ground to go what would be 1/4 that distance direct.
With that being the case, I'll be using 14/4 CL-3 wire for those runs, and twisting the 2 pairs together. Same amount of cable in terms of total feet, but the wire is a little less than 12/2, and wiring together should yield a lower resistance than a 12/2 on its own.
The other option would be to find some type of raceway, or 3/4" conduit. With them adding another 3/4" of sub-floor on top of the existing sub-floor (for height matching, and leveling), I could run the conduit first, and let them add the sub-floor around that. Wouldn't make a ton of sense for the run behind the couch, but would work for the longer runs. Then again, that may piss off the installers with now having to make cuts for that. Guess I could always use a router to make out a groove for a track, once the sub-floor is down to help them out with that. A little leveling compound across the top to even out any gaps around the track and work out any height issue.
Second option would make for shorter runs, but may be more hassle than it's worth.
Of course I still have to decide between doing that and just throwing a soundbar setup at it. The replacement lot of flooring shows up next week on Tuesday, and install wouldn't start until at least next week Thursday. Since I haven't been contacted yet for the install date, it most likely will be later. So a week to 10 days at least to get it settled. If not, then it would be under and around with longer runs if I ended up going that route.