I heard him conduct in a couple of concerts here in Philadelphia. I too, agree that he is a well-rounded conductor. His M5 was featured in one of those concerts, and done very well. The Casella discs I have in my collection, and they're very good. In one of the two concerts, he did Casella's Symphonic Excerpts from "La Donna Serpente" and not being familiar with that composer, I was very impressed with that composer's orchestral writing, as well as the performance. That performance led me to purchase the four Chandos Casella disks.
He definitely ought be a very good fit with the National Symphony. Interesting, how he follows Eschenbach as Music Director, who used to be up here in Philly.
Wade