I'm guessing that since these are licensed cards that you wont find any takers to do this, if you want to do it yourself for your own personal use with your own hardware then no-one can stop you but dont release the files publicly.

Same deal with converting Roland midi stuff, its all licensed and thus youll have to do it yourself with your own hardware, if you dont own any of this hardware then you are out of luck as no-one will risk the ire of copywrite law or the mods here at Vogons.

There are already XG SoundFont files. You can find them elsewhere. They are not the same as what you get from the XG MIDI Engine, but many find them acceptable.