PGMusic has already gone to the trouble of making a demo that compares the way a song sounds with different sound sources.

DEMO PAGE

Maybe they would grant permission to link to their demos from your web site. In the final analysis, you just want to make the point that sound quality in MIDI files is largely a function of the sound source. The songs used wouldn't have to be yours to make that point.

Why spend valuable time reinventing the wheel?

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0