Welcome to the PG Music forums and the BIAB community, Horahack. Technically this post should be in the BIAB for Mac or Windows forum, but let's get your question answered first. I can't answer in detail now as I'm working, but want to assure that someone will get you sorted.

I will say that the solution will be somewhat complex. You will end up using two programs, as BIAB only has one audio track available and you're going to need at least two. (Fortunately you have the other one--RealBand, which is designed to work hand in hand with BIAB.) Another tricky part will be matching the tempo of your original track. But I believe you can get substantially started in BIAB and go from there.

Good luck,

Richard

"My primary musical instrument is the personal computer."