Mann often collaborates with Danny Elfman, and toured with Oingo Boingo, playing keyboards. He has also worked with Jeff Lynne and Electric Light Orchestra. In 2002, he played George Harrison's parts in "Concert for George", playing along side Eric Clapton, Jeff Lynne, Paul McCartney and Ringo Starr. He also played keyboards on Harrison's last album, "Brainwashed".
In addition, he has written string arrangements for several artists, including System Of A Down, Red Hot Chili Peppers, Regina Spektor and George Harrison's son Dhani Harrison's band Thenewno2.