One thing that is important to keep in mind when using MXM files within SketchUp is the type of tiling that the creator of the MXM file specified.
There are 2 types of tiling possible: Relative and Meters.
The basic idea is that Meters (which used to be known as "RealScale" in older versions of Maxwell) allows the creator to set up the MXM texture(s) to tile at a specific real-world size... this requires the UVs for that object to be 1 meter X 1 meter. The way this is accomplished inside SketchUp is via the Maxwell>UV Coordinates context menu -- here you choose your UV projection type (Cubic/Planar/Spherical/Camera) and set the projection size to 1 meter.
maxwellUV.jpg
However if the MXM is set up to tile using Relative (typically with a value of 1 and 1) it will automatically tile at the scale and aspect ratio of the UVs created inside SketchUp. The easiest way to control this is to choose one of the texture images used in the MXM and create a new SketchUp material (setting the scale in the SketchUp material to whatever you want as your final).
Unfortunately, often without MXED you will not know if the MXM is set to Meters or Relative tiling, and as you can see you would take very different actions in SketchUp to get proper results.
Best,
Jason.