Hi,
You should see ModelConverterX a bit like GMax, it produces your model, but in the end you will have to use a placement tool to position it.
As Dick mentioned there is an option now to produce a XML sample when you are exporting for FSX, if you are exporting for FS2004 the sample XML file is made by default.
As Tom mentioned the common approach is to put the MDL in a library BGL file, after which you can use all of the common placement tools to position your object. On my wishlist for ModelConverterX I have a function that will allow you to enter the placement from within the tool as well, but that might take some time to implement.