Hi
Just to add to that,the 2019 version of BIAB has Biab as a plugin .
If you go to preferences in Reaper and to plugins prefs and scan for the biab vst then you will be able to open ur saved biab box directly into reaper.The wav files will be generated onto individual tracks for you to use.
Another option is to save your backing tracks as midi or xml files on your computer and load them as a media file into reaper.It will distribute them on individual tracks and you can put a virtual instrument of ur choice on them .
Spitfire audio do a set of amazing free virtual isntruments called Labs by the way.urs Hugh