The Montage can respond to MIDI Files setup for GM and XG protocol. These files will "tell" the Montage to select sounds from the pseudo-GM Bank. And while the Montage is NOT an official GM nor an XG product, it will select an appropriate sound based on the Bank Select and Program Change protocol. You will then need to either substitute your own selections and generally tweak the setup from there.

Load the .mid file to the Montage, set the Montage to the "Multi/GM" Performance (this places it in a one-Part-per-MIDI-Channel form required for GM/XG use).