also your picture shows you are trying to use usb not the mix output and
your cables are in mix1 and mix2 not in mix3 as OP said and they do NOT have usb outputs on them
Try this for more info on how to do whatever it is you are actually trying to do
First of all if you select a mix and want to listen to the selected you need to hit the PAFL button on the mix master and with headphone plugged in you will hear whats on that mix.
You do have a cable plugged into the mix 3 output on the mixer, where is the the other
end of that cable connected to?
If you are using the USB B connection for your output to the computer and you actualy want to send your mix 3 to the computer using track 3 on the USB you will need to change that to mix 3. Touch the #3 block and use the encoder knob to scroll through the choices till you get to mix 3 and then hit apply.
@Val
The USB patching to the Qu is carried out at the computer and the channels you patch to will appear on the Qu at the USB-B input for the matching channel number.
e.g. If you patch to USB channel 5, then switch the input source for input channel 5 to USB-B you will receive signal from the computer.
Then it works like any other input channel, as USB-B is just a source for that channel in the same way as Local (built-in sockets) or dSnake (remote sockets).
The outputs of the Qu are labelled with the output/mix channel which feeds them.
So in this case you need to send the input channel you’ve patched to back out to Mix3.
For example:
Patch computer output to USB channel 1
Switch Qu input channel 1 to be sourced from USB-B - press the 'Fn' key when viewing the preamp screen of any channel to see all sources, ensure that USB-B is selected as the USB input type (rather than Qu-Drive), touch the channel 1 box and change this to USB-B
Press the Blue Mix 3 key to show sends on faders for Mix 3
Turn up input channel 1 and the Mix 3 master level
(Processing before you send the signal out from the Qu on either the input channel or the mix is optional, but presumably you’re using a DI signal and want to keep it as close to the original as possible so you could also just turn all processing off)
Cheers!
Keith.