This is what they say in a thread on the Studio One forums
Basically you have two modes:
Mode 1 = old behavior = Sub bus processed all children tracks + main bus process all child tracks except sub buses.
Mode 2 = passthrough mode = Sub bus processed all children tracks + main bus process all child track including buses.
i got confused as well by the anwsers. About children and not children. Im not used talking in terms of children for mixer tracks in a bus.
Ive noticed what it do.
If you have a mixer bus-/aux- track with a couple of tracks routed to that bus and you use passthrough active on console shaper then it will
ignore the bus-/aux- track and apply mix fx to the tracks routed to the bus/aux track instead.
if passthrough is disabled it wont apply any console shaper on the tracks that are routed to the bus track. instead it will apply
console shaper for the summing signal of the bus aux track.