Rob, I know your tender feelings toward RB. I don't interrupt any conversations on RB when it lives in it's own space. I never did. Regardless of our mirror opposite views on it , this discussion should focus on BIAB + recording Audio into BIAB. This subject is important to me personally, and I share frustration of OP and all those who want a straight forward, user friendly approach. I feel it is simply wrong to send people elsewhere instead of advocating to standardize this in BIAB. Which should be no brainer.

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Cerio,
While I share your sentiment on "It’s better to use each tool for what it was designed for", there are exceptions. This is one of those. Most responders share views based on their own workflows and don't consider that other users might not want to get involved in learning a whole new software to just get a few tracks of audio into BIAB the easy way - and be done. Would you, yourself would want to learn another software if all that you needed was to record your vocals or single instrument (1-8 tracks) on top of BIAB arrangement? I definitely would not.