The audio out will not stay selected on my USB out, it will play a few seconds then switch back to the HDMI out…
The USB out is going to my receiver and the HDMI is going to the TV to use as a monitor. The sound will play through the TV speakers using the HDMI but I want it to play through my receiver and speakers that are connected to my Mac Mini with USB
If you can provide a video of the switching happening and the exact local time in your country (e.g. 12:37 on 4/15/19) that you experience this behavior, that would also be helpful.
What USB speakers are you using, what is the model/manufacturer?