Alex Greenwald, Michael Runion, Z Berg, James Valentine, Jason Boesel JJAMZ Five successful artists go from musical friendship to supergroup  It’s a steamy summer afternoon, and Elizabeth “Z” Berg is in a van with the rest of the newly formed band JJAMZ, ready to embark on a 24-hour trip from Austin, Texas, to Billings, Mont. “Well, I’ll get a book read. That’s a positive,” Berg chuckles. “Somehow I am built for tours, which is good...