File Extension SYX File Format MIDI System Exclusive Message SYX stands for MIDI System Exclusive Message. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Delete messages and time log Convert file to SMF on Yamaha YPG235 keyboard Channel roundup: Who's gone where?