Lots of interesting questions here. First, welcome to the forum.

I often use BIAB to arrange for a full jazz stage band. There are built-in harmonies that can be used for three, four, even five part harmony. You can see a section on the screen at once. I export the arrangement as MIDI files to a notation program where I prepare the scores for individual instruments.

About your reference to a problem with note duration, I can't answer that until I know what you consider to be the problem. I do not have such a problem, but then, I never did with BIAB going back almost 20 years. Let us know what you mean.

As far as sound, you should tell us more about your existing system. You can get good sounds from hardware modules or from software synths. I recommend you start a separate thread for that, post what you have, what your budget is, and anything special you might be looking for. As an example, Garritan makes a program called Jazz & Big Band that might be just right for you, but we need to know more.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.