Mixxx is a software for live performances. I think instead of trying to shoehorn Mixxx into being an automated streaming media player, you should use something much better suited for this. For example, MPD has all the functionality you need built-in. You could even use it on a headless system, e. g. an Raspberry Pi. Another alternative would be using VLC, which should also be capable of doing what you want. I think Mixxx is just the wrong tool for your use case.
Mixxx is a software for live performances. I think instead of trying to shoehorn Mixxx into being an automated streaming media player, you should use something much better suited for this. For example, MPD has all the functionality you need built-in. You could even use it on a headless system, e. g. an Raspberry Pi. Another alternative would be using VLC, which should also be capable of doing what you want. I think Mixxx is just the wrong tool for your use case.