Topping d90/a90/pre90/ext90 confusion

As far as I can see only the d90 can have its output configured to line out. De a90 only has pre out. Leaving the ext90 aside as that one is just extra, how do you use this stack?
Or are you not supposed to use the a90 and pre90 together?
I haven’t seen any examples in the marketing info, but the only thing that seems logical would be: d90 → a90(passive line out pass through) → pre90.
But passive pass through is not mentioned anywhere.
And if the pre90 is only intended for adding extra inputs, why give it a volume nob?
And they seem to have missed a trick not allowing multiple xlr outputs.