Although the first post says 'simultaneously', the title and request doesn't imply that both outputs need to be active at the same time to me.
100% volume is the same as Fixed, at least according to my RME dac's bit perfect test.
So my answer is yes, you can have 'unaltered pass through' on one output and volume control on another without having to toggle that volume setting, and you could use presets with custom volumes to switch.