Mo, you seem to be using a file that has not been prepared adequately for the purpose. I just checked the file from LearnChoralMusic, and found that it has all the 8 choral parts in separate "tracks", as it should. I prefer the files from the column titled "UNemphasized" and use a player software that allows you to choose the degree of "emphasis" freely. What is "Choirparts"?

This side discussion should not distract us from the actual topic - a really charming poem, all the more so for those who (like Yours Truly) have tried to learn those old notation systems themselves. Yes, there has been some progress since, and some helpful standardization.