Sounds like an MIDI events issue. You might try to open the notation window and click on # (event list) and change velocity levels there. I haven't had the need for it myself since I made my midi files in another program and the volume is ok after importing. I checked the eventlist though and even if it doesnot to seem to support the midi controller 7 for volume, you could still try to change velocity. If the event on the midi track are really a volume issue, which are added into the midi file, this trick probably won't work, unless anyone else knows if and how BiaB can use controller 7. As far as I could see, the eventlist only works for the melody and solo tracks.

You could also try to work in RB, but that also isn't easy I think, but you can record fader movements on the tracks, so you automatize (is this correct English?) the volume.

Third way would be to adjust the volume and or velocity controller data allready in the sequencer you made the songs with (if you still got that).

I'll be back...