I've used BiaB for almost a year...not an expert. This PG Music video highlights the 'drag and drop' Drop Box function...it starts at about minute 16:00.

https://www.youtube.com/watch?v=XOvqyQ27tuA

Guitarhacker walked me through his method too. Nice guy. I use Sonar X3 also, and good, bad, right or wrong, when a song is worked out in BiaB and ready for export, I open that BiaB .sgu file with Real Band. Then from RB I save it as a .seq file. In Real Band I add/generate more instances of instrument tracks as needed and then I drag them into Sonar.

I found exporting from BiaB takes a long time and the volume was lower than if I exported from RB. I don't know why. I have the 2014 programs.

This older video was helpful to me also.

https://www.youtube.com/watch?v=kKkN78DfWRQ

This same author has two videos 'Cooking the Tracks with Real Band' that helped me too.