I´m not on my SQ right now, but i should be something like this:
first you must ensure in the I/O section the “SQ-Drive” is the USB source, not USB B.
Still on that same page use the TieLines Tab to the left of the screen. Then choose Slink (provided you use the Slink port for your stagebox) also on the left side.
In the upper row you can choose the output. There Local, SLink,…and USB. You tab on “USB” tab and route your signals.
Please remember, this is from memory. Don´t be mad at me if it´s wrong. But maybe it helps guiding you in the right direction.
Cheers