Welcome to the macProVideo forums :)
Reversing a MIDI file doesn't produce the same effect as reversing audio.
A MIDI event can be a note. That note does not contain sound as such, it is information which then triggers a sound in a synth or a sample in say the EXS24.
So reversing a collection of MIDI notes would reverse their performance but not the actual sound you hear triggered.
To reverse a MIDI note (let's say it's a cymbal) you need to bounce it to an audio file and then reverse it in the Sample Editor (to hear the cymbal play backwards).
Hope that helps,