However, there are various degrees of heteirim: During the year we need music to calm our nerves. Also music during the year music is permitted for a s’udas mitzva.
But it could be that according to the M’chaber and Rav Moshe, the music that they assur all year is lively music, not classical or dirges. So perhaps this type of music would be permitted during s’fira as well (it IS muter according to Rav Saloveichik and my Rav). Can this logic be extended to an avel all year, and during s’fira. I don’t think anyone will give a public heter, however, maybe yes to a private heter.