If you're keen, there are some subtle things you can do to the tuning if your software/hardware supports it. Fingered brass (trumpets, euphonium, tuba, French horn etc) use non-equal temperament with perfect harmonics between certain notes. So (after transposing a score in Concert C to Bb) the ascending notes for a trumpet:
middle C, G, C, E, G, A#/Bbb, C... are all perfect harmonics, hence the jazzy Bb (about 1631.5Hz), giving you harmonies that you can't usually get on a keyboard with piano tuning.
That combination can be repeated for a couple of semitones down from that:
B, F#, B, Eb, F#, X, B
Bb, F, Bb, D, F, X, Bb
A, E, A, C#, E, X, A
From there you can sort of play it by ear and adjust a few notes if they don't sound quite right. And even use a soft-synth to add a tiny amount of random pitch variation.
Edit: sorry, I missed the bit about the problem not being the sound, but you're welcome to try those things out anyway and see if it inspires something. I used to play a bit of trumpet so I'm very fussy about keyboard brass sound.