USB audio out of outputs 3/4

Hi there,

I have got USB audio backing tracks going into my QC (from my phone), but can’t get it to come out of output 3 or 4 to my speaker. It only comes out of the headphone output.

I’ve also tried switching the 1/2 to 3/4 outputs in the output screen.

I’ve had a look at the output screen, does anyone know if it’s possible?