There are many ways of looking at spiritual music.
Ultimately, all music is equally spiritual. All phenomena – including all music – is God, Buddha Mind, Existence expressing, manifesting and exploring itself completely and perfectly. Bach, Sting, an Indian chant, heavy metal and a song made up by your five-year old are all equally spiritual. They are all complete and perfect manifestations of God in the present.
Then we have the more conventional view, where some music is indeed more spiritual than other. They may express an opening, devotion etc. This view would say that chants and devotional music is spiritual, while most other music is not.
And then the view I find more interesting: that the music coming out of contractions and confusion may be the most spiritual music. After all, it allows me to come to myself as space & awareness while listening to it. I can say “yes” to the “no” inherent in the music. I can allow the expressions of contraction and confusion unfold within me, within myself as space & awareness, as all other phenomena in the present unfold within me. It becomes part of the rich and fluid tapestry. And this is maybe the most valuable contribution. I can explore and familiarize myself with my fuller holarchy of being, in a setting that is not likely to harm anyone. This makes it easier for me to do this in daily life, when these contractions and the confusion arises within this small self rather than from music. From this view, heavy metal and similar music, is the most spiritual. Seriously.