Which one of those replaces a Denon AV receiver to accept a bunch of inputs in various formats (HDMI, phono, optical, etc) including Dolby Atmos and ARC support to drive a multi-room 15.4 speaker system?

You could perhaps consider looking at some of the class D amps coming out of CN. Remarkable stuff considering the price and power output.

SMSL has some good, well reviewed products; as do WiiM and quite a few other brands.

The Audio Science Review forum (1) has objective measurement based reviews of many of the newer amps, standalone and integrated.

I’m using the SMSL AO300 to drive Boston Acoustics VR3 floor standing speakers in a study, and they’re sound as good as they did when they were on an older Yamaha amp, or a Denon integrated amp.

Edited to add: most (none?) of the class D integrated amps can’t do Dolby -(licensing, I suspect, is the main issue here), so you’ll need to get a receiver in the middle for HTS though.

Edited post edit (sorry!): turns out Wiim streamers can now do 5.1, so some options are slowly emerging. (2)

(1) https://www.audiosciencereview.com/forum/index.php?forums/am...

(2) https://faq.wiimhome.com/en/support/solutions/articles/72000...

Get an integra pre amp or receiver

Don’t think they are available outside the US.

Just pick better brands for your receiver.

I have an Anthem pre and an LG TV, both of which are blocked from accessing the internet, and I have none of these issues.

I think the point is with Samsung acquiring these other brands there are now fewer options. Denon AVRs have been solid options for home theaters, particularly if you have many different inputs. People buy them because they want a Denon/Marantz. If they wanted to buy Samsung that option is already available. The concern is Samsung will mar the brands, removing semi-affordable, quality options and forcing people that don't want Samsung bloat into potentially even more expensive alternatives. You'd run into the same issue if Samsung acquired your audio equipment manufacturer of choice.

Yes, exactly. There are a couple of companies making home AV hardware. But not a lot of them. And across a lot of industries the different players are all getting gobbled up and turned shitty much faster than new competitors can replace them.