Here is a explanation of the phrases/words in context:
Is the highest voice in a musical movement.
in die Stille gelauscht werden:
I am not sure what it means...
I guess it means the sound fading into silence, when you have stopped singing. But I don't know what an "Abeeyo" is.
Plural for ending sound.
It means that the two voices can overlap in the case of slower chanted "abbeyo" phrases.
Hope this helps you. But be aware.....
I don't know much about music.