I don't know if it exists already, but what I would like is a Bluetooth mixing app: say it is installed on my phone, I connect to speakers and I can play music

I don't know if it exists already, but what I would like is a Bluetooth mixing app: say it is installed on my phone, I connect to speakers and I can play music from my phone. Buddies around can connect by Bluetooth to my phone and "play" some other track to me. Then a fader allows me to mix both tracks to the speakers.