Vquestor, Yamaha has not made it easy for you to convert their module/software XG Wavetable to other formats. You would need to sample it and save it in the new format - not a very easy job at all. You may find some attempts of this on the internet. A search my lead to something, e.g., http://www.hammersound.net/

.... and there may be others. I am not certain if this site has XG converted wavetables. It has GS Wavetables.

In the end there are many soundfont wavetables that are quite good. You can always change out the voices you don't like to something better. I tend to use GM500 (a 500 mb Tascam GM Wavetable). There are others at 1GB that may be of interest. I tend to use these for my accompaniment wavetable so that I have minimal editing to do to play midi or style files.

For my lead and melody voices I will continue to use the top of the line samplers and voices.