I've found the first vault (containing "Sasha's first loss"), all but one figment, all the emotional baggage, combed the area for any sign of a second vault (because apparently, there is one, it's just really good at hiding), and I can't seem to find it anywhere.

Could someone tell me which area it's in and the general scenery around it so I know where to look?

On the shooting range, go to the side of the cube with all the shoeboxes and the sliding measuring tape deal.

The vault is on one of the other sides of the cube.

This is a very minor thing regarding Sasha's level...
When you go through Sasha's level for the first time, in each of the different "shooting galleries" you shoot the Censor spigot once and it reappears in another location in the gallery. Shooting it for a second time closes the shooting gallery and the next one opens.
But in the last shooting gallery (the four flaming arcs with a central tower) this doesn't happen. You only have to shoot the Censor spigot once and it doesn't reappear in a second location.
Of course, next the Boss comes. I just thought it was a little odd that they didn't have a second reappearence of the spigot in the last gallery since that's what happened in all the previous galleries.