As I posted on BR forums a while back I don't think volumes should be changed from the old system at all. We have already compensated for volumes when we made our ABC files. Changing volumes now will make all our files sound different when played in game. So if as you say, you are trying to even out the volume levels, then when I play an ABC file that I have turned the volume on lute down a bit to play softly in the background and turned up the volume of a horn to play the melody and you for example have turned the volume of lute up and horn down or even left it the same. Then you have completely changed the way that file will sound when played in game. The lute will now be dominating the song. Get the instruments in tune? Yes! Fix any wonky notes? Yes! But I say leave the volumes as they are in the old system. Does anyone get what I'm saying or am I just babbling nonsense?
I get you perfectly and I was one of the first to advocate exactly what you are advocating. You can change the tone of the instruments and their tuning. But if you start changing the volumes, then all the work we have done in the past with all our abc files have been in vain.