Can I apply more than one material to an object? For example, I have a cube and would like one face of the cube to have a different material than the other faces.
You can do that if your Cube consist from separate planes. You can create it in Ps and after exporting it as 3D object import it into Dn. Then you will have separate layers or objects in Dn. This will allow you to use Selection Tool as Ussnorway suggest.
Or you can build it from 6 separate planes Models in Dn and do your task. For working with whole cube you can also group all object
example is cardboard, red glass lid and metal insides
one tip when selecting sides with the Dimension wand is to first make the model larger (hold shift while dragging one of the [red, blue, green] bars)... you can always make it small again after adding the side materials