Opening Old Metro Document Files Because Output Setups saved with Metro document files override Outputs Setups saved in the Preferences setting, you will have to reassign Outputs to the appropriate channel and track if you open an old existing Metro document file but want it to adhere to a new Output Setup—even if that new Setup is contained in your Preferences setting (see also Change Ports). Note: If you open a METRO document file that was created using a different MIDI system or OS (e.g. OS 9 without OMS, but are currently using OS X with MSS), you may have to do some manual reassignment of the Output ports in the Instruments Mixer window, as well as the Output assignments to tracks in the Tracks window. The Change Ports dialog is handy for the remapping of port assignments.