At some impressionable age in my life, someone made this comment to me:
"So and so is such an amazing player. He can play SO LOUD!"
I cringe at the impact this made on me! Specifically, I cringe at the number of orchestra auditions I took where my evil doppelganger self took over my brain, saying that we needed to show the committee that I can play SO LOUD.
The list of loud orchestral excerpts for trombone is a bit longer than the list of soft excerpts. In my mind, however, the king of the loud excerpts is the first movement of Mahler's 3rd symphony.
Apparently, many students feel the same way about this excerpt because I've heard all too many people lose all good judgement in the all-consuming pursuit of ..
PURE SONIC POWER!!
For many trombonists, the possible antidote to this mindset may come from the vocalises of Marco Bordogni. Faced with these pleasant, lyrical pieces, they naturally try to show off their most lovely sound.
So here's the trick: take the notes of that Mahler and play it using that Bordogni lyricism.
Mind you, this is a practice technique, not audition advice. However, my hope is that some of the Bordogni habit of beautiful phrasing and lovely tone will rub off on the Mahler.
While you're at it, try playing Tannhauser faster, softer and prettier. Same concept.