I put together a paper on converting your FS9 gmax aircraft to FSX Native using gmax. The .pdf is attached for your reference.
I also recorded a Youtube video going through the process in detail if you prefer a video approach.
https://www.youtube.com/watch?v=D5eLKM6AeAk&index=1&list=PLfy8rn3tQYdeBx4EqQjY5x3jbHNhKc_MR
This is still evolving but the basics are in place.
Hope it helps.
I also recorded a Youtube video going through the process in detail if you prefer a video approach.
https://www.youtube.com/watch?v=D5eLKM6AeAk&index=1&list=PLfy8rn3tQYdeBx4EqQjY5x3jbHNhKc_MR
This is still evolving but the basics are in place.
Hope it helps.