Another option that might apply to some that have a fairly modern Home theater receiver is HEOS. Often some of these receivers will support a separate "room" zone aside from the main x.1 HT TV setup via the HEOS protocol or just thier own proprietary means. You can hook an Echo up to that zone, then run speaker cable to your separate zone. Typically you sacrifice one of the surround channels speaker outs so you may need to drop from 9.1 to 7.1, etc. The main drawback of this is running speaker wire from the HT receiver to your new zone. Seldom is the unit anywhere near the speakers to be placed and running long lengths of wire discretely can be a challenge for some homes. Also, the volume controls may not always be ideal or even remotely adjustable. I pretty much wrote this one off in favor of the dedicated equipment options.
I have this as my set up, but kept to myself because it doesn’t check all the boxes OP is looking for.
That said, I love it.
Denon HEOS/HOME WiFi integrated receiver, run through a 4-channel Tivoli speaker selector with independent volume control and on/off for each channel, essentially setting up 4 zones (screen porch, living room, kitchen, grill area/back porch).
Running the speaker wires wasn’t the worst, and was a better option than supplying power for speakers.
Aside from selecting zones/channels, it can all be controlled through phone app, which is awesome.
And as I said in another thread, I love the HEOS/HOME ecosystem, the receiver is basically like a Roku with lots of apps built in.
Denon also has HOME speakers that can be added- connect via WiFi, and can play same source or different source as the amp, and function as standalone smart speakers. Again also supporting lots of music services.
Edit: most of these do support 2 zones, that I think can be run independently