Ok, I've said this before in other threads, but I think it applies here also so I will repeat it as succintly as possible.
God made everything.
Therefore, God made music.
When he was finished creating, He looked at His creation and declared it good.
Therefore, music, is by default, good.
Not all music today is good. Some people taint their music with lyrics contrary to what God declares is good. But in absence of these taints, music is still good. Instrumental music declares the glory of God just as much as music with vocals praising Him.
If a secular band writes an instrumental song, it praises God. They may not intend for it to, but by making another way for everybody to see something God made, they glorify God.
I highly suggest a read of Addicted to Mediocrity by Franky Schaeffer. There's a review of it
here that summarizes a few of the basic thoughts in the book.