On the Alesis the input gain knob was set to the 2 o’clock position, the trim know was set to the 2 o’clock position and the master output knob was set to the 10 o’clock position. At no time was any of the gains close to being maxed out, which in turn will always result in a lower noise floor. (White Noise). You can achieve the same results with the 2 or 4 Channel Alesis Multimix USB Mixer as well.
If you need to run your feed in stereo, you would just create two buses or keep all your channels panned to 0 in the X32 Rack. You could also use a Matrix but it is really not needed. The most basic feed you can create is to use one bus will everything panned to 0. The best information in this video IMHO is “Gain Staging” as well as “Simplicity”.