To make the conversion process easier I use sketchup and make sure any groups or components in the mesh have been exploded I then build a up a collection of all the groups, components and faces within the mesh. I then iterate through all the individual items that make up each group and component multiplying the transformation matrixes at each step of the iteration so that the transformations flow down to subsequence child items remembering to record the transformation matrix along with faces vertices at each stage. When I say iterate I believe I wrote it using recursion.
Once I have built up a collection of faces and transformation matrixes I simply apply the transformation matrix to the vertices when creating the direct x mesh file.
Hope this helps it’s been a while since I wrote the code.