From the ALSA wiki
You can play MIDI files in several ways - see the page PlayingMidiFiles for more details. One way is to use a MIDI keyboard or instrument connected to the MIDI interface of your soundcard. However, if you do not have a MIDI keyboard or instrument available, you can still play MIDI files using a software synthesizer (aka softsynth) which converts the MIDI data to audio samples and plays them on the PCM device of your soundcard. Some examples of software synthesizers are:
GusSoundfont has information on gt, a version of timidity that does 4 and 6 channel sound using Alsa.
patched source files for using Timidity++ for 4 and 6 channel sound with Alsa are at ftp://ling.lll.hawaii.edu/pub/greg/Timidity51.tgz.
add more, please
Retrieved from "http://alsa.opensrc.org/SoftSynth"