My understanding is that at the Watsonville performance, they put the offstage brass in the balcony of the Mello Center there.
However well the overall performance came off, I seriously question their decision to put the small brass (and percussion) ensemble in the balcony. Mahler's instructions in the score are as follows:
[Es] muss so schwach erklingen, dass es den Character der Gesangstelle Celli und Fag. in keinerlei Weise tangiert. Der Autor denkt sich hier, ungefähr, vom Wind vereinzelnd herüber getragene Klänge einer kaum vernehmbaren Musik.
[It] must sound so faint that it in no way affects the character of the melodic lines in the cellos and bassoon. The composer has in mind roughly the sounds of a barely audible music sporadically carried across by the wind.
In every performance I've heard (12 and counting), this effect has been achieved by putting the players backstage, sometimes even in another room with a partially-opened door. By putting them in the balcony, they're closer to much of the audience than the players on stage. Even at pianissimo they would be too loud, too present, and too localizable (sonically and visually) to seem like "a barely audible music sporadically carried across by the wind."
I've heard the oboe & English horn dialog in the third movement of the
Symphonie fantastique spoiled by just such a miscalculation.