[1][2] He has served as the musical supervisor for numerous productions, including Cats, Moby Dick, Chicago, Blondel, Follies, and Into the Woods in the West End; several international tours of Les Misérables; and the United Kingdom tour of Martin Guerre.
He orchestrated and arranged the music for Mamma Mia!, which garnered him his first Tony nomination, prior to Billy Elliot.
Koch conducted the BBC Concert Orchestra for the intro music, the interval act "Jupiter, the Bringer of Joviality," and the French entry, "Où aller" by Marie Line, which initially was performed entirely to a backing track before the decision was made to incorporate the orchestra's string section.
[1][2] Koch recently orchestrated five operas by Richard Thomas, a project commissioned by the BBC.
[4] He and collaborator Nick Gilpin own and operate a music production company that has been responsible for numerous television programs and several recordings, including Jerry Springer: The Opera.