Not sure what you mean by "doesn't work" -- I assume you mean it slows SketchUp down. Regardless, the basic function you are asking for has been requested before, but the plugin does not currently provide any specific workaround. There are various ways you can work around it yourself, though, for instance:
- say you have an Arroway MXM named brick.mxm, which uses several huge textures
- pick which of its textures you'd like to see in SketchUp, and make a reduced copy of it
- make a SketchUp material named brick, put your reduced texture in it, and apply it
- turn on Auto MXM in the plugin
When you render, the plugin will find
brick.mxm and use it, instead of generating a material from the
brick SketchUp material. As far as not being able to manipulate textures in Maxwell, if you mean Studio, then yes, you can do that; see the UV Sets topic on p. 106 of the Maxwell Render manual. You can use any number of different mapping types (cubic, planar, spherical, etc.) for generating UVs in Studio -- it is much more powerful than SketchUp in this area.