My son also plays in a Christian rock band and some of their music is pretty high energy but they also play Christian worship music that is delightful to the soul. They often play this worship music for the congregation and everyone loves them.... even one of our 90 year olds
Youth is part of our future and this is how they show their love for God and they are passionate for him. The youth of today is an integral part of any church and this is a great way for them to reach out to others.... by way of their music. God will work through them.
Your son, his band and your youth group appear to be a very positive energy to your Church and the pastor knows it! Perhaps the boys could also learn some of the Christian worship songs, i.e. Hillsong United type songs and play it for the congregation sometimes so that some of these folks also get to see another side of their music?