What is in the box file, text or an array?
For text you want something like:
VAR BOX1$
LOAD "TXT:BOX1.VX" FALSE OUT BOX1$
For a number array, something like:
VAR BOX1%[0]
LOAD "DAT:BOX1.VX", BOX1%, FALSE
Box1.vx was the filename, right? If not update with the right filename.
Bad news on the voxels. If you want to show those files in your program you will need to make a 3d engine to draw them. That gets difficult fast. I haven't used that program before but I would guess you load a 3 dimensional array and each square is either empty or a color code. Voxels are basically 3D pixels.
For the background, you want something like the attached right?