If the open floor plan is on a slab, then I suppose that the three channel makes sense.
Our house now has a crawl space under the room, so I went with a Lyngdorf as I haven’t had a HT set up, and the XLRs allow one to run the signals to amps closed to the speakers, and use minimal length speaker wires.
Anthem, Marantz, etc. all do the same basic stuff, so if you need three channel that is easier than 5,7 or more.
Basically if you are happy with 3 channels, and also physically limited to three channels… then why change things?
If you were me would you consider a major audio upgrade to separates or the latest AVR? Or wait until a TV change?
I think planning it now makes sense.
And by the time the TV goes, you should be closer to having a good plan.
There are so many options, and constraints, that it is not easy to find the optimum.
But as you say:
Set up is old technology but still delivers great entertainment.
So it doesn’t seem like much can happen upgrading a 3 channel to a newer 3 channel. I would save the $ for then the TV dies and not rush it myself.
Plus the supply chain issues still have me awaiting gear… so nothing is complete, and I am over a half a year into it.