Ross. You can do all your MidiFile editing within the 9K.
I won't go into the full details but....After loading in your MidiFile as if to play it, go to left of screen select Digital Recording Song. Select existing song and make your alterations as required. You can change volumes, pans, voices etc: and you can save back to floppy. Suggest you give your edited version another name so as not to alter the original in case you wish to refer back to it.

Graham UK (9000pro)