Try looking through the MSDN forums for DirectX, or in the documentation that came with the DirectX SDK that is on your PC, they usually have a few samples dedicated to working with their file formats.
I had the same trouble with my skins getting screwed up by exporting to directX from dif apps, I use XSI myself though...
I have found 2 ways of getting things from my chosen software package to a useable .X format(useable meaning it preserves the texture sets, shader info etc)
First I should state what I believe the main problem with most .X exporters for 3D most packages is... they Screw the textures up.
This is due to the fact that earlier formats of the .X specification only supported a single UV set.. meaning you could only have 1 texture set on an exported model, which was a pain, meaning you export it, then re-wrap it etc, now however, the .X format supports as many UV sets as you want it to, and all the Shader/Material relationships you want aswell, problem is in how most .X exporters dont implement more than a single UV set still.. The only one that I have found(freeware) is for MAX and its called PandaSoft PandaMAX DirectX Exporter. it supports upto 8 unique UV sets per .X file exported, and decodes the shader/material relationships etc and exports them properly aswell....
The first solution I use to get soemthing from my 3D modelling app to DarkGDK, is to export it to a format that I can import into 3DMax(using XSI as my modeller, I use the dotXSI format for exporting, it has its own SDK and its almost the same as .X, being template based).. I then import my model into 3DMax(i dont own 3DMax, a collegue of mine does though, so I use his
) and using the PandaSoft DirectX Exporter, I can export my model directly, and it can be loaded from there straight into the DarkGDK... the reason this works for me is that there is great support between 3DMax and Softimage XSI through the SoftImage dotXSI file format and associated Crosswalk platform SDK(which has plugins for max to import dotXSI files)... meaning I get my model into max and it is exactly the same as it was in my original modeller(XSI)..
The second solution is to make a "custom file loader" for GDK... Mike Johnson has written a great tutorial on the subject, its stickied to the top of the DarkGDK forums thread. Using those methods of getting data from a custom file, into DarkGDK, it would be simple to use a Maya format natively, and just load the straight into the GDK... specifically its the .FBX format for maya isnt it? I think they have an SDK for that particular format, meaning the reading of its data into memory is easy and using that file format in place of the format that Mike uses in his tutorial and still following the tutorial should be a piece of cake.
I know that is kinda backwards from your original idea, of making an exporter for maya using the .X file specs.... but just making an importer for GDK using the .FBX format which is maya's native format and already has an SDK I think, could be a little easier(once you get the data into GDK, you can save it back out as a .X or .DBO format file if you should choose to), both ways of doing it though are valid, just comes down to personal preference.
If it ain't broke.... DONT FIX IT !!!
