Turn a notation file into a playable MIDI — exactly, since both formats already know every note. Get the MIDI, an MP3 render, and each part as its own practice track.
MusicXML and MIDI both state pitches and durations unambiguously, so going from notation to performance data loses nothing musical — every note lands exactly where the score says. What does not travel is the notation layer: page layout, note spelling, articulation marks and text all live in MusicXML and have no MIDI equivalent. That is expected and harmless if what you want is something to play.
Compressed .mxl files work the same as plain .musicxml — they are just zipped. Repeats are expanded so the MIDI plays through as written; if a score's repeat marks are inconsistent (which happens with files exported from scanning software) we play it straight through and say so on the job.
The same pass produces an MP3 render, one track per part, and 85%/70% practice speeds that keep the original pitch — so a choir can rehearse from a MusicXML file someone shared without anyone opening notation software. The score plays back in the browser with the notes highlighting in time, and you can loop any passage.