Disklavier

Hello,

I was wondering if someone could help me understanding the nuance 
between the "GM" and "XG" type of instrument set found on different 
midi files, and how to apply my choice when making Disklavier disk?

Is there some that sound better on a Yamah Mark unit?
How about if I change the style of them when making making disklavier 
format file, with Giebler on else?

Any comments appreciated.
Thanks you.