I'm looking for a network media player that is capable of outputting multiple audio streams simultaneously. I have Monoprice 6 Zone Home Audio Multizone Controller and Monoprice 4 Zone Home Audio Multizone Controller daisy-chained together to provide me with 6x10 audio matrix. Currently it's running from 4 separate Chromecast Audio devices. But Chromecast Audio can be flaky, takes a while to connect to, and requires a phone/tablet to start streaming.
I would like to replace it with a single device, that can do either 4-5 separate simultaneous streams and would also provide bridged mode, where all outputs would output the same stream (nice to have, monoprice controllers can do it themselves). I mostly stream from Spotify, so support for Spotify remote is a must. Chromecast support would be nice too. Bluetooth and local file streaming would be good to have, as well as possibly support for other internet streaming services, like Amazon, Google, TuneIn, etc. Pretty important that it would have an accessible API and can be controlled from the web/apps.
I've been searching for something like that for a while, and the only thing that I found that comes close is MusicBox 6 but it's pricey and I can't find much about it.
My back-up plan is to setup a small Raspberry PI farm using PI MusicBox and have a sound card attached to each one. But MusicBox doesn't work great with multiple instances (there are some hacks/workarounds, but they are all not great).
I'm pretty sure something like what I want exists out there, but I just can't find it. Any pointers would be appreciated.