The "monk" clue is a bit strange - monks are by no means the only people who sing Gregorian chant (the best answer is probably cantor, although that has too many letters obviously). I was quite confused what answer the quiz wanted for a while - maybe a better clue might reference monastic musical liturgy or something.
Saw ____sonic, knew this was about music, and couldn't get past JJ Fad's Supersonic. Still haven't read the clue, didn't matter that super is five letters.