Most interesting duet I've heard in a while:
https://www.youtube.com/watch?v=rLUjnitQPZg
The Shoichiro Hokazono channel is worth listening to. There's an especially nice Sparke 1st Euphonium concerto played with a wind band:
https://www.youtube.com/watch?v=MmIRkSXEo8o
I really love this concerto, especially its beautiful slow movement.
John