I thought that poem looked familiar, that's why (I recognized the stuff at the end like you did but couldn't remember what it meant lol). I noticed some of those files, I wish I'd realized it sooner because I wonder if there are more than what I saw. I'm sure the black and white bit in the middle of Monika.chr can be turned into something as well, but I'm not quite sure how to go about it.
I also had a really creepy thing happen where I restarted the game, deleted Monika, then restarted again and Sayori freaked out (restart again for maximum effect). I'm was legit very very upset about this, I don't know why I'm playing this still so late at night, haha.
*edit*
Someone on the Steam forums decoded Sayori's OGG file. I thought there must be a way to make this into something other than an OGG, but heck if I know how they did it.