You need to export to a .VGM file using M1 or similar emulator. The VGM file format is basically a dump of raw data written to the sound chips. From a VGM file you might be able to convert it to MIDI with a conversion tool, I've had some success ripping notes from NES music. It will give you the pitches and you need to figure out the note durations yourself.
Since you're interested in System 11, here's a rip of Black Knight 2000:
https://vgmrips.net/packs/pack/black-knight-2000-williams-system-11b