OSMC (RPI+ALLO DAC) as bluetoothspeaker very loud output

I have a rpi3 + ALLO BOSS DAC set up. It works great to play stuff from my nas or add-ons, but when i want to stream my phone to osmc (for example spotify) i can hear it, but its incredibly loud. Setting the bluetooth volume to 1 on my phone (trough the kore app) does not change a thing: its either on and very loud or off . I’m a bit stuck here.

You need to set the volume on your phone. There’s no volume control on the Pi that can adjust playback from phone to DAC.

setting my media volume (and all other volumes, just to be sure) on my phone to 1 is still not helping. still incredibly loud.

What sort of phone? My Android phone works fine (phone->vero->HDMI but phone->Pi->DAC should be no different).