Ah Raymond, and you probably think that you're chasing the Holy Grail! I've spent a lot of time on this, and have a couple of answers - depending on the types of Midis that you're listening to there may be an answer.

(1) If the Midi files you are playing have defined rhythm tracks with unarpeggiated chords, then Jammer (Shareware) does a brilliant job of interpreting the chord (no matter how complex) placing the whole score of chords on the screen and scrolling through them as you hear the tune played. There's a lot more detail I could go into, but it's probably better to wait for other responses to your question. Jammer is produced by Soundtrek, and it's only the most recent versions that have this feature.

(2) ABCMUS1.1 uses an algorithm to calculate the chord value for files in ABC format (which can be converted from Midis). This is a nifty low cost program and very useful for ABC users for a variety of reasons, but I am hesitant to commend it for your particular needs. I was initially sceptical about the chords generated for Celtic dance tunes, but having been recently inspired by the Double bassist and guitarist from Lunhasa I am keen to re-visit some of the apparently bizarre chords dreamed up by this program. The author is Henrik Norbeck (who contributes to this forum from time to time).

Hope that this provides a start for you.

Regards
John