JE, if you have the Windows version of BiaB, then you also have RealBand. I think this is the best and easiest option for you to undertake your task.

You can lay the 3 MIDI files out on three separate tracks, then cut and paste as required. RealBand is a DAW, and has the tools to undertake this. You can also output to a file that can then open/run in BiaB


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