Generally, I export the BIAB as wav files, import them into my DAW (I use sonar) and then record my parts.
This is what I would suggest.
I haven't used Audacity since forever but seems to me if you've actually exported a BIAB backing track(s) as a
.wav you should be able to import them into Audacity without issue....unless I'm missing something in your original post.
I export all BIAB tracks as individual wave files to a folder and import from that location into the DAW.
This is how I've done it for my BIAB songs. (I'm on Sonar also)
I know nothing about the H2 Zoom audio interface recording quality which may be something to consider for your purpose.
Carry on....good luck.