It was my understanding that a .rmd was some kind of "zip" file containing 3 .x's. That's what you get when you import a .rmd with the utility, at any rate. Also, to my knowledge, there are no distinct texture files from the .x's. And lastly, the reason I don't think the isd file will work is that you'd need 3 .x's to get the same view from all zoom state, I believe... But try-it for yourself