A little clarification needed.
Can I use the Line Return only, as a Line In, without Preamp Out and without anything connected to the front?
I know the manual say:
Line Returns are normalled to the channel 1 and 2 preamp outputs, so they take precedence over the corresponding Mic/Inst input on the front of the Quantum 2626.
Power user tip: the Line Returns can also be used to input line-level devices that have their own volume control; synths, channel strips, preamps, etc.
But it still remains a little unclear to me.