Choosing GM instruments when exporting MIDI

I’m trying to export a project to midi. It the song has four different instruments. Typically when I open a midi file in a program such as Quicktime 7, each voice/part is played by the proper instrument. Unfortunately, when I open my exported track, each instrument has been changed to piano. How can I maintain my instrument choices when exporting MIDI?

You need to assign program change numbers to each track, and these must adhere to the General MIDI (GM) standard. Take a look here.