Hello,
I recently added the ITS suite of music programs to the GitHub
repository:
http://github.com/PDP-10/its
They are: MUSCOM for generating binary music data from source files,
MUSRUN for playing the data on a PDP-6, and BIG which does a lot of
things. I also updated a PDP-6 simulator to play sound.
Someone else mentioned a music program on the DECUS tapes:
http://pdp-10.trailing-edge.com/decuslib10-01/
MCOMP seems to be an adaptation of MUSCOM.