As I've been finalizing some jazz projects this week, I revisited a few tracks where I wasn't thrilled with the timbral balance between The Trumpet and The Trombone, and found in a few instances that the Bass Trombone did the trick. The range is similar but the timbre is quite different; less splatty. Sometimes that's what you need to better blend with other winds. Don't forget the Bass Trombone; many do not know or understand the instrument. The Contrabass is the one that is actually lower in overall pitch range.
From Wiki:
"The modern bass trombone is pitched in B♭. Its tubing length of 9 feet (2.7 m) is identical to that of the tenor trombone, but it has a wider bore, a larger bell, and a larger mouthpiece. These features generate an overall darker, weightier tone that speaks with a more assured authority in lower registers when compared to the tenor trombone."
As for the Tuba, for consistency's sake I replaced my VSL Tuba on one track with Sample Modeling, and had to work at it a bit as the articulations and phrasing are not quite as realistic as the laborious work done with VSL key switches, but overall the timbre and especially the controllable vibrato, sound more realistic in the jazz context and blend better with The Trumpet and The Trombone.
I also have one Orchestral Horn part in one of the jazz songs, and The French Horn got used vs. VSL. It's actually a very expressive instrument with a warm and natural timbre that doesn't get splatty.