I have a new music library which comes with it's own sequencer. It is called MMD. It uses OpenWatcom C with DOS target installed.
MMD supports 8 simultaneous channels. It supports Adlib\SB, MT-32 and
General MIDI.
MMD stands for Michael's Music Driver.
Play and Mseq both take the same command line parameters:
Play\Mseq [SNG file][driver]
Driver number
1 - Adlib\SB
2 - MT-32
3 - General MIDI
It can be downloaded here.