Thanks for your reply, and for the clear explanation for creating the aux strip for this purpose. I finally realized that an aux channel was the only way to do this and appreciate the quick and easy instructions for doing so.
During this process I began wondering if some kind of routing device, thereby using the headphone amp and perhaps getting an additional pair of monitors, might be helpful. Would a passive device (open to suggestions) color the sound, or is the aux send just the best way to audition different monitor mixes (using the ensemble's outputs)? Thanks so much.