If EZ-Track doesn't let you save as .mid, you can use EditTrack to convert your files; it can load EZ-Track songs.http://tamw.atari-users.net/hyart.htm
(scroll down to the bottom)
To save you reading the docs: start up EditTrack, load a .SNG file by left
-clicking on the Load menu item, save a .MID file by right
-clicking on the Save menu item.