First, the Surface window is missing the maximize button that that is wrong.
I record most live events using RM16AI and Capture.
The recording level is set by the gain knob.
the mix is set using the channel sliders.
if you are recording you have to keep selecting channel and then adjusting the gain.
you rarely need to adjust channel mix, just the gain trim.
if you could toggle all slider modes between channel fader and channel gain things become interesting.
outline faders in red for gain, green for mix
select gain mode, and set all the gains so that the recording levels are correct.
select slider mode, and adjust the sound mix as desired.
select gain mode.
now the sliders are the channel gain, and they adjust the recording level and the resulting mix.
if you are recording, and in gain mode, every adjustment is of channel gain.
you now have 16 gain controls in front of you and can adjust all of them.
the sliders are perfect for that.