"Palm" - The Soul Rebels
I do not understand the purpose of bonus tracks, but here is a perfect argument for why The Soul Rebels are the most significant modern brass band from New Orleans. The harmonic makeup of "Palm" suggests jazz and R&B influences, the song's bridge struts away from the traditional marching beat, and the arranging of the instrument voices broadens the overall sound. The Soul Rebels push the envelope of what marching bands are capable of playing.
The borrowed bVI chord, the Bbmaj7, always packs a punch. It is a powerful interval of either a major third down from the tonic, or in this case a minor third up from the IV chord. Add to it the sus9 rub of a C against a Bb, two notes not found in the original key that pleasantly resolve by half-steps in opposite directions, and it can mimic a V-I cadence. In the assumed dominant A7 chord, the Bb and C act as a b9 and #9, respectively, but the Bbmaj7sus9 creates more of an impressionistic resolution.
I assume that the trombone solo is played by Paul Robertson as he is the composer of the tune. The cleverness of it, for soloing purposes, is the fact that the advanced harmony is based around the simple D major pentatonic scale. However, the Bbmaj7sus9 chord could be based around the D natural minor scale, similar to Miles Davis' use of modal scales. When soloing over this tune, use the D major pentatonic and then flat the third, sixth, and seventh degrees (F, Bb, C) for the Bbmaj7sus9, and it will sound like you know what you are doing.
Here's a YouTube video of a brief lesson explaining the impressionistic sus9 chords. In it, Frank Zappa's marimba player, Ruth Underwood, explains how he trademarked this open sound in his music.
Recommended Reading: Cat's Cradle by Kurt Vonnegut. Published by Dell Publishing.