Usually one should leave a little headroom, when you mix tracks together to a stereo mix. The biab mixer has a scale from 0-127, that might translate to - 60 (or nothing) dBu to +12 dBu. IMO: I guess 90 is around 0 dBu, with a normalized RT or Drum audio file, so you'll have 12 dBu headroom maybe as volume playground. Can of worms here BTW ... -F