I don't have any experience with whole-house audio systems, but it really sounds like a disappearing technology to me, being replaced by systems like the Sonos you mentioned.

From the looks of it, they require a pricey and complicated multi-zone A/V receiver/amplifier at the wire termination location. I happen to be looking at A/V receivers now, and most of the consumer grade ones I'm looking at are all 2 zones maximum. To get into the ones where there are enough zones to handle each room in a big house separately, they start to run into money and your selection starts to get much narrower.

I suppose if your main TV and movie-watching location was in that basement where the wires terminate, then it might make sense to make use of the wiring by spending the extra dough on a multi-zone receiver. I'm guessing that the whole point here is that you can either pipe the same music through the whole house from the same receiver, or, pipe different music to different rooms by rerouting inputs and outputs? This sounds like the complexity of managing all the input and output sources would be daunting.

Personally, I never have a need to have the same music playing through the whole house (though I know some folks might like/want that feature). But if I want to play different music in different rooms, then I would rather just have a phone dock or a bluetooth receiver in each room. No need to worry about whether the switching system is on the right inputs or whatnot.

Example of a system for this sort of thing: https://www.htd.com/Products/Whole-House-Audio/Lync

That system does look kind of cool because it includes things like integrated intercom and front/back door communication features. I suppose if I had a large mansion I might want something like that.