CadBotte,
The XPK (package) file is the file that UGNX and Solid Edge interoperate with, and what UGNX to UGNX from two different installations (not networked) transfer back and forth. They retain the relationships within UGNX.
You want to use the parasolid file over the IGES file only if...
You can do the 2d conversion in a batch mode mode with a simple script. Print out to CGM, open CGM, save as dxf. You can also write other commands into the script, such as changing layers or line types, color by entity types, etc. This way you can do an entire project from TDM at one time or...
jrmartin,
You are in deep. I have been involved with what you are trying to do for many years. There are no true "bi-directional" translators for what you are trying to do. At best you will be able to end up with a dumb model (no history tree) and a non-associated 2d drawing. The best...