.MUSX File Extension
What is a MUSX file?
A MUSX file is a notation file saved in MIDI format and created by Finale, a music notation program. It contains music notation data and additional information that can only be read by MakeMusic software. MUSX files replaced .MUS files.
To create a MUSX file simply select File → Save As... with your document open, choose your save location, name the file, select the MUSX file type, and click Save.
NOTE: The MUSX extension was introduced in Finale 2014.