This is what I believe with the little experience I have but you'd need to check on my answer:
- when playing files, I do not need Matlab and did not try from within Matlab, but when I play a midi file from windows, the standard windows (or any other) player plays it and if I plug my keyboard on the USB port (cord bought from Amazon for 5€, works great) the sound is redirected to my keyboard without anything else to do. I believe that will be the same if playing the midifile (but probably not just any sound file) with a Matlab command (unless Matlab translates it into a soundwave or something, different from the midi standard)
- to do MIDI in real-time (I know that's not what you're asking but you may still find some answers to related questions):
https://fr.mathworks.com/help/audio/musical-instrument-digital-interface-midi.html?s_tid=CRUX_lftnav
Musical Instrument Digital Interface (MIDI)
Create, send, and receive MIDI messages
Audio Toolbox™ enables you to create, send, and receive MIDI messages. You can interface with MIDI Control Surfaces and MIDI Devices in real time.
- Regarding latency, I don't know
