So, my current whole house audio is powered by Chromecast Audios. Unfortunately they no longer make them. But you can still get them new off eBay. I know because I just bought 5 more (unopened from Japan) as part of finishing our basement
Mine feed two 12 channel (six room) amplifiers. I’ve got a mini in each room whose default speaker is the associated CCA and it works great. I have speaker groups so I can ask “hey Google, play music in the basement” and all rooms play.
Previously I used casatunes. They don’t do this anymore, but I bought a PCI card from them (it was a sound blaster hardware) but it was a 6 channel sound card and associated software that ran on windows IIS. It allowed both hardware and software streaming. I liked it but it never supported Google music and eventually I switched to the CCAs
I’m sure a lot of people’s self hosting journey started on junk hardware… “try it out”, followed by “oh this is cool” followed by “omg I could do this, that and that” followed by dumping that hand-me-down garbage hardware you were using for something new and shiny specifically for the server.
My unRAID journey was this exactly. I now have a 12 hot/swap bay rack mounted case, with a Ryzan 9 multi core, ECC ram, but it started out with my ‘old’ PC with a few old/small HDDs