Hm, the problem is, I'm no 3ds max expert. Until now I thought I would need separate UV-Coords for all 12 maps. But if I would use the same UV-Coords for all 12 maps, my problem would be solved. However, I don't know, if someone more experienced with 3ds max would appreciate the option of individual UV-Coords for all maps :/ (maybe some advanced techniques require a special UV arrangement). But that question should probably be posted in a different forum ^^.
But with such a small VertexFormat splitting the streams would then be unnecessary, wouldn't it?
Your last suggestion is exactly what I am looking for.
So you suggest, I store the UV-Information in a texture-like-format and then access this information in the vertexshader via a texture sampler? So I guess my exporter for 3ds max could already store this information in the proper format. However, I read that sampling from a texture is slower than simply accessing data from the input struct. Is it true?
Here is some more code to show what is frustrating me. I'm copy&past-ing a lot which is exactly what I want to avoid :/. (I have not yet compiled it (I'm in the middle of rewriting parts of my code :/), so there might be some minor errors.)