I will add that if you buy a SMF or Midi file made by Yamahamusicsoft.com or midi spot that are basically Yamaha, or made in a PSR S or Tyros5, the Midi file if is made by what I mentioned, automatically will ALSO follow the chord progression....just have the styles (preferably already in the Registration bank, made sure that have the same tempo, just as a precaution, because the tempo is sync automatically).....
I use Taylor Swift (Shake it off) Midi file that I got from Yamaha, and made up up to 8 different styles, and during the song, I change the styles, is incredible that you can hear the song with an entire different arrangement.
My 2 Cents
Manuel