Read through the Rambam, Shulchan Aruch, etc. You will see that any heter to listen to music is not pashut, even year-round and certainly during the 3 weeks. Obviously, a seudas mitzvah such as a wedding or even a chol hamoed seuda would be different.
The a capela that they have nowadays is also very not pashut.
People seem to take for granted that concerts during Chol HaMoed Pesach are muttar but there are actually those who would assur it due to the fact that it is during sefira…
I’m not saying that you should follow every chumra in the book but it is important to understand that some of the psakim we have are kullas, not necessarily lechatchila, and are often misinterpreted and taken too far.