If I understand you correctly, you wish to convert Yamaha XG midi files to regular old midi files. The main difference is how the sounds are arranged in banks and numbers(Yamaha XG) and the regular general midi (GM) single bank with 128 sounds. I have seen web sights with sound lists for XG and GM, but can't recall them. There are other differences besides sound arrangements between XG & GM but that should get you started.
Hope this helps.
K J