I have this to say- you stated that you listen to it because it brings you peace and you are respectful of songs. that is not misusing it.
Now, we bring in intent. the tape was made to preserve the songs and language in a way that the young people would be able to learn them, and keep them alive. it was not the intent of making them to bring anyone who listens to them peace, but to teach, and preserve. using them in any other way is misuse.
using certain drugs to treat ailments, or pain is fine, but using them just to get high, is misuse(not a good analogy i know), not only do we call it misuse, but it is officially called drug abuse. the abuse comes from using them for other than their intended purpose. In this case, using the tape is not not abuse, using the tape for a purpose other than it was intended, is abuse. in this case, spiritual and cultural abuse of a people.
there is some wonderful music that is calming and relaxing that are freely available. perhaps you should get one of those. and mail the tape you have back to one of the people it was intended for.