I can tell you a way to do it but I will have to mention that terrible REAPER and I might get jumped on and have to leave the forum again for another 6 months frown
In the song setting dialog there is "Avoid transpositions in RealTracks".
https://stash.reaper.fm/v/48388/Import-frozen-SGU-MGU-realtracks-drums-tracks-GUI.zip

https://stash.reaper.fm/v/47372/ReaTrak-amagalma_Write-project-markers-or-regions-as-media-cues-to-selected-items-active-takes-source-files.zip

make a copy backup of your wav files in the RealTrack folder and store elsewhere
if you don't have wav files just batch convert the folder wma > wav
create a chord track in Biab in a key
generate up the soloist guitar track
freeze track and save
Run Import-frozen-SGU-MGU... script in Reaper and open the saved frozen SGU
load the chords into Reaper, see link below post #804821 Working In Biab & Reaper Simultaneously and Instantly
load the tracks
insert the track
you can insert a cue into the wav file by placing cursor where the chord occurs with ReaTrak-amagalma_Write-project-markers-or-regions..
from Action list run View: Toggle show media cues in items
Biab will try not to transpose so look for transpose amount at the top of the Reaper items, allow for this when add chord names as cues in the wav file.

The .bt1 are just beat files like reapeaks in Reaper. The info is in the XT2 ST2 in C:\bb\Soloists.