Carolyne
perhaps an analogy might help.
i'm not a architect..lol..so apologies..but here goes...

when a building is built..
firstly a foundation n framework is erected , then all the
building is built up from that.
then finally the prettying up of the building takes
place to make it hopefully pleaseing to the eye.

in many respects a song is no different to the above analogy.

think of biab as building the framework and bed traks of the song.
and realband as fleshing out lots of extra traks and details and
finally adding the song pretties n iceings.

so one way of working would be to flesh out the song basics in biab,
then import the song into realband where you have 48 traks.

if you compartmentalise like this it might help you,
viz song basics in biab, and fleshing out the added traks and
things like upfront lead vocs in realband etc.
then final mixing and creation of the final stereo master in rb.

the beauty of this is biab songs will open in realband.

this is just one way of working.
i'm sure other folks have other ways.

you know the old song..
"love and marriage go together like a horse and carriage" ??..lol.
you can think of biab and RB the ame way.
they are like "mates".
together they can give you a very powerfull
solution for creating songs.

retired puter engr....powertracks on amd......NICE !
"what is the black art of audio engineering ?"
my silly songs...motagator.com/bmanning
see my tips in the tips section.