Philip Quast has sung both male roles. He sang Archibald for the Shakespeare Company's 2001 production (http://www.amazon.com/Secret-Garden-Rutledge-Turnlund/dp/B00005BCD6/ref=sr_1_1?ie=UTF8&s=music&qid=1237599484&sr=8-1/), with Christian Patterson as Neville. He and Anthony Warlow sang in the Australian production.

It is a gorgeous song. It is a shame that there don't seem to be many male duets in music theatre.