I just set up Navidrome and connected to my phone with Symfonium. So far I am loving the experience.
I would like to get this going in the home. I was wondering what people use as far as speaker choice. I would love to listen in the home outside of the phone or headphones… are there apps that integrate in Android TV or AppleTV… what is everyones setup? Thanks.
I have Kodi (LibreElec) running on a Raspberry Pi 4, which is my main media center connected to the TV, and can also be used to cast music via UPnP there. In addition I have two boxes (one RPi 1B and one RPi Zero 2) running Raspian (basically a Debian Linux) and on that mpd with upmpdcli as UPnP front-end, so I can cast music via UPnP there.
Of course I have an amp and speakers connected to each RPi.
Setting up Kodi is relatively easy, for the mpd/upmpdcli setup you need to be a little more versed with the Linux command line, so a more technical solution.
As a more mobile setup I also use a Bluetooth speaker connected to the smartphone, but I guess that was not what you were looking for.
There are of course more “out of the box” solutions, e.g. with Chromecast, but others will need to describe that.
Splinter, if you don’t mind can you tell me about the rpi. I wanted to know whether the rpi 4 is actively cooled using a cooler? I’m thinking of self hosting stuff with a rpi.
I cast to Sonos devices and Chromecast devices 
No active cooling. I have a Flirc case for the RPi 4, which made from aluminum and acts as a passive cooling device.
I tested it back then because I read that the RPi 4 gets warm. After 20 mins with full load (cpuburn) the CPU core temp was at 73°C and the case was so warm that I did not easily want to touch it anymore. But it did not get hotter. I think at 80°C the CPU throttles itself.
In real life (Kodi/LibreElec, playing 1080p non-HDR h264 or h265 content at max) it never gets that hot, CPU load is nowhere near the limit. The case is constantly warm though (idle CPU core temp when nothing is playing is about 48°C), so I guess it works as intended. I am perfectly happy with the setup, running it for over three years now. And it was a massive improvement over the RPi 1B I used before 
My set-up is using fairly old kit. Model B Raspberry Pi server now also running Navidrome. Symfonium casting to a Sonos Play:1. This suits my needs for a small back room.
I’m probably not the only Sonos refugee here. When I had to rebuild my server (lost my SSH passwords) the S1 app would no longer connect to the local music library - Symfonium to the rescue!
I used the RPi 1 model B for years to run Raspbian and upmpdcli, but in the last months replaced them with RPi 3 model A (which is very similar to the RPi Zero 2 stats-wise). It does not make much difference for playback, but updates go way faster and the built-in wifi runs more stable than the USB wifi adaptors I used with the RPi 1.
No idea how many more years I’ll get out of the RPi but it’s given better service than the Android TV box (running Kodi) I had. Updates were indeed slow but wifi not an issue as it and attached hard drive sit right next to the router in the hallway.
I used them for ten years or so and still trying to figure what to do with them now Before I had the RPi 4 I had an Intel NUC which broke after a couple of weeks. The RPis are real work horses.
Ouch. Those NUCs weren’t particularly cheap.