I also use BIAB as backing for live performances, usually senior centers and retirement communities.
I play tenor and sing. I use bass, piano or guitar(alternating choruses) and drums. Occasionally I insert a melody as a backing for my playing or singing. So far I think my description of what I do is in line with the the general discussion of this topic. I use a Fender Passport to do the mix at my home and also use it live at the venue.
This is what I think I do differently and has not heard mentioned. I pan the bass hard left, guitar/piano hard right and drums/melody center.
The Passport has RCA stereo inputs so the left and right channel volume, fx, bass/treble levels can be controlled to suit the room.
Last week two days in a row I performed in two entirely different rooms. My first song is a background selection that I use to evaluate the sound characteristics of the room and make the needed adjustments.