sfmorris-I am not sure what is classified as heavy rock exactly...I have never been into metal, but my fare typically was a huge dose of classic rock, Genesis, Yes, Pink Floyd and the likes, as well as various jazz, folk, acoustic, some electronica, a smattering of classical, and really, I felt like my Model 4's did it all pretty well.
Maybe with really heavier rock/metal, the speakers are not going to plumb the depths of hades, or give you that gut thump in the chest some may want.
On the new Model 9, I have no idea how it sounds, or what is different about the drivers, crossover, etc., as I haven't heard it. It looks nice in that typical Swedish way. Rather pricey, but maybe worth it, I don't know.
The best thing you can do is try to get a listen to them and hear if they fit your tastes. As I have said though, give them a bit of a listen, don't make a quick judgment on them, as they are a different perspective.