Knowledge of the Alpha channel opens a world of possibilities with the Composite map in 3ds Max.  Composite maps and contained as many other maps as you want respecting the Alpha channel transparency of each individual layer.  Note, however,that there is a big difference between Composite materials and Composite maps and we're talking about Composite maps here.

Composite maps

Let's say you're creating a material for a racing car or a complex floor pattern and you need to have flexibility in the maps used, the placement of the maps, and the size of the maps.  You'd start by placing a Composite map in the Diffuse Color slot of the material and setting the number of desired maps, which can always be changed later.

Each of the new slots in the Composite material would contain one of the bitmaps to be applied to your model. Now, if you apply a UVW Map modifier all of the sub mapswill be under control of this one modifier and you'll have a jumble of images someplace on your model.

Map Channel numbers

In your Material Editor, each map that is using Explicit Map Channel Mapping type is automatically assigned Map Channel 1. You'll also want to clear the Tiling check boxes in the Coordinates rollout for each of you sub maps so that they don't repeat.

In the Modify panel, UVW Mapping modifier, Channel area, the Map Channel setting is 1, so that this UVW Map modifier sets the coordinates for all maps to have Channel 1 in the material.

Matching Map Channels in the material with those in the UVW Map modifiers

Now you simply add more UVW Map modifiers to your object; one for each of the sub maps you need to control in your Composite map. Make sure that both the map's Channel number and the corresponding UVW Map modifiers channel number match.  Use the Show Map in Viewport button in the material editor to display the map in your viewport as you adjust the mapping coordinates of its UVW Map modifier.

There are 99 Map Channels available which should be more than you can ever keep track of.