The vault would look something like this:
I intentionally made this room dark because it's a vault. It's meant to have little to no light. Almost all of the Xycraft blocks you see here are made with Dark Xychorium. The 2nd floor of the vault uses Light Engineering Bricks. The ceiling and some of the walls are made with Dark Engineering Bricks.
On one side of the wall, there's a light switch to illuminate the glass casings and tool racks
The problem with Xycraft blocks in general is that the patterns are too strong to be used as a general purpose material for a wall or ceiling. But here, the glass casings and the tool racks lessen that effect, making it easier to look at.
On one end of the room, we have the display case for armors.
The casings are made of Xychorium Shield, primarily because they have an interesting pattern which gives an impression that it's a ruin from an advanced ancient civilization. I make use of nether brick slabs as accents, as they serve both as a step to access the armors when the glass case is open (they can open and close via pistons), and to give contrast to the strong pattern of Xychorium Shield.
And finally, the second floor will be housing some of the stuff I want to display in chests and portable tanks. An example:
Those are orange structure blocks, and they work well as pedestals for these crystal chests.