I had the good fortune of rehearsing a piece with an ensemble a few weeks ago. It was one of my own compositions written specifically for the ensemble. The group is getting ready to perform the piece at the Association of British Choral Directors National Convention in Oxford in August. The ensemble has been singing the piece off and on for about a year. When you go into that situation, you normally don't have to worry about pitches and rhythms. This ensemble sings at a level that doesn't require you to address a lot of fundamentals about breathing and even vowel issues go away after a year of practice.
As I listened to the group, I found that they sang quite beautifully, and they were working pretty hard to listen. When you have a group making music at that level, your job is to invite them to listen to each other in new ways that will give them insights into the music. Your first tool for inviting people to listen is still the gesture. If the gesture fails, you may speak.
I find that the main issue when listening to a group of highly trained performers is simply one of inviting them to make space for others. It is often the case that an individual gets so excited about their own part that his/her focus turns to the beauty that they are creating on their own at the expense of the beauty of the whole. In this situation, it is the conductors job to make space for the whole and to help the individuals see how their part fits into the larger context.
For me, it is enough to invite the musicians to listen in a new way and trust their musicianship enough to make the necessary corrections.
It is an excellent lesson for life. Even when you are excited about the cool thing that you are doing, you need to make room for others.
Here is a performance of the piece from earlier this year.