I'm also a comeback trumpet player and I use a lot of playalong cds. My wife plays flute so we have a lot of the same cd playalongs with books. While the sheet music is obviously in different keys for the trumpet and flute, the cds are in the same key. All of the cd playalongs that I have are written for a C instrument. The same is true for fakebooks unless you buy one for a Bb instrument (these are not common).

You might want to check the video for the Real Band features. In it they show you how to put the chords in for an audio (mp3) file. They use the ACW to do that. However, I confess that I have not done what you are trying in BIAB. I have done a lot of arrangements for songs in BIAB for my wife and I. I always do it for a C instrument first. Then I save the file. Next, I transpose the melody up an octave for the flute and print out the notation. Then, I undo that transpose via the Edit menu. Next, I transpose for the trumpet by changing the key signature as needed. I then print out the notation. Finally I undo the transpose. The end result is that we now have the BIAB song, and notation printouts for both the flute and trumpet. If you play without charts, you don't need to bother with any printouts.

If I'm just starting from scratch before any chords are entered, etc., I use BIAB. If I'm working with existing tunes, tracks, or whatever, it's easier for me to use Real Band. If you have an existing BIAB song and all you want to do is change the style, then BIAB is the way to go. YMMV.

Cornet Curmudgeon