There seems to be a lot of opposing going on between the songs(when the top of a sound wave happens to match the bottom of another with a similar amplitude), which cancels each other’s sound out, I’m guessing that’s why long lasting, consistent sounds like Lia’s voice in Heartily Song makes it easier to be heard.
just a guess
oh and, it was a horrible experience for my ears…
and also…It can be heared at the end that you’ve put Little Busters! twice, I think the other one was the Ecstasy version from LBEX 
