Thank you very much for the insights presented here.
I have a vocal/guitar stereo track that I have used ACW on - and when I take it into BB and generate accomp. parts, the tempo/chord changes are way off. This is not a complicated song... three chords, 4/4. So, what I did was go back into ACW and use the tap (+ key) to try to align the bars to the first beat - and that got it WAY closer, but not exact enough. I'm used to playing in a band (keys) so staying in the pocket isn't usually a problem but this is tough.
I must be missing something here. I'm not a beginner to music or recording, but I am to BB - so much to learn.
Please, if you could step-by-step this (aka, ACW for dummies) because what you describe doing is exactly what I need to do (but I also need to retain the original audio.)