cherrybim – Most frum people who sing in choirs are memorizing relatively simple songs and harmonies. But for a large orchestra where each person has to do his own ‘kneitch’ on his particular instrument at different places in each song, and has to be told what to do by the one arranging the music, it is unheard of that each one of the musicians simply memorizes his part. The levi’im had a fairly large orchestra, it wasn’t just singing (see Arachin 10a-11a), so it’s hard for me to believe they didn’t use some form of notation.
That which you say these notes would be meaningless in terms of recreating the sound is not true at all, first of all the same way there are people who can decipher old languages they could probably figure out this too – and they do, as we have songs from ancient Greece. Second of all it’s probably easier to decipher a musical language because there are a limited number of scales and it’s all mathematical; all you’d need to do is guess a little bit until it makes sense.