Love Germany. I am a rock/heavy metal fan and have variously been to gigs in Munich, Cologne (twice), Berlin (3 times), Hamburg, Bremen, Osnabruck (twice), Lichtenfels, Kaufbeuren, Ludwigsburg. Also did the Christmas market in Stuttgart but no gig.
Two thoughts on Munich which is a great city. If you can bear going to a Bundesliga game Bayern are at home to Augsburg on Sunday 8th March. Appreciate it might not be your thing and you probably know already.
Also if you want somewhere to eat in the city and you are a large group, go to the Ratskeller. It is absolutely massive, the food is fantastic, the staff are very very welcoming. Possibly one of the best places I have ever eaten at.