iOS GarageBand audio input/output control

Hello,

I have an external USB audio interface (focusrite 2i2) that I run mics to, which I would like to use on my iPad GarageBand at the same time as the sound output being sent to my Bluetooth headphones. That is- GarageBand receiving input from the audio interface (via USB), then sending output to headphones.

Is there a way to do this?

On Mac you can just open GarageBand preferences and select audio input/output devices separately, but there is seemingly no control over this on iOS...? It just connects automatically to an audio device, and I can’t find a way to control which.

I’m hoping there is some settings tab or something I have missed- in the GarageBand app or settings app. If not, and it is impossible, I will be extremely disappointed.

Thank you!