In addition to "secrets" there are "mysteries" - like why doesn't anyone make an "Amp" except Sonos, and why is it that one so darn expensive? I guess because they are the only one.
Sonos's one plays nice w/ Sonos's ecosystem, but if you don't need that there are other solutions.
If I were looking to undercut it, I'd look for a two-part combo, like a $99 WiiM Mini streamer coupled with something like the $329 Emotiva BasX stereo amp. That's not going to get you any of the Sonos-specific ecosystem woo, of course.
https://emotiva.com/collections/amps
and parts-express...
I've owned things from all of these places so there's that I guess :)