The music must be in WMA format.
If AllowAutoConfig = YES, you don't need the entries in the MXM.xml, if the programs are in the immediate subdirectories underneath MXM... but you should make MXM_Entry.xml entries in each directory to define the game info.
If you have a MXM_SS.* (png, jpg,wmv,bmp,gif or tga) in the game directory, you don't need to tell MXM what file to load as the screenshot.