RE MIDI file defaults. Well-written MIDI files should contain a 'GM RESET' command at the start. Unfortunately, most amateur files don't, and then they will pick up any settings left over from the last file played.

One of my handy MIDI Utility programs, MIDIFIX, allows you to add a GM reset to an existing MIDI file (It also lets you edit global settings such as volume and Pan for each channel).

HARMONY always puts GM Reset into any MIDI file it creates).