I am using two Cannon camcorders hooked up to a Revesun HDMI 2x1 Multi-Viewer. I also have a Logitech 920 attached to the USB port. I looks like turning USB audio on mutes the HDMI audio. Have you seen this before? BTW sometimes I see an error message that the HDMI audio is out of range.
When you enable USB audio the HDMI audio will indeed no longer be used. The two audio sources are not mixed together, you are choosing one or the other.
The HDMI audio range error is just a warning, it doesn’t break anything fortunately. If you have fully updated the unit the range we allow before showing the warning was increased, so make sure that you don’t have a prompt for an update in the top left corner of the screen when you have an HDMI monitor/TV connected to the Webcaster X2 output.