thanks for your post !
looking and seeking around, have found this:
pMusic seems playing midi files at the conditions that another non-midi (i.e. .mp3 file) file is present in the right-hand window; if only a .mid file present then no play.
/root/.pmusic/tmp/exec looks like:
#!/bin/sh
LANG=C timidity -Ow -o - '/mnt/sda6/273.mid' | ffmpeg -i pipe:0 -f au - 2>> /root/.pmusic/tmp/ffmpeg_output | aplay 2> /root/.pmusic/tmp/aplay_error