Hiya.

XSI (at least verion 4, the one I use) can export .x (textures, objects and animation) with a plug-in. However, when you import the .x into MED (A6), the FIRST and LAST frames need to be manually deleted by you. I'm not sure exactly why, but if I make an animation in XSI 4, say from 0 to 60. After exporting and then importing to MED, I have frame 0 to 61. Frame 0 seems to 'reset' the model to 0,0,0 world co-ordinates; at frame 1 it jumps to where it's supposed to be. Not sure why, but oh well. You can happily delete frame 0 and the last one to get the animation range you need/want. For some animations, this may require you to add an extra 'dummy frame' at the end of your animation sequence when in XSI.

Hope that made sense! Bottom line: delete frame 0 and last frame after importing .x, and you're good to go! Oh, and you will probably need to scale the .mdl. I'm still trying to figure out what scale factor I want to use, but if you use the "1 unit" mesurements in XSI, you will want to multiply by 12.8 in MED to get a 'normal sized' model (so a XSI human model that is 6 units tall would become 76.8 'units' tall in MDL format).