DubiousKB, and others:
Note that, in most cases, volume adjustment using an AH slider fixes this issue for both the "too soft" guys and the "too loud" guys, so it IS technically possible for AH to do this. The problem currently is, as stated, if you increase volume to hear player A better, player B becomes too loud, and if you decrease player B, player A becomes inaudible. And requests to players to adjust don't usually work; it's just human nature.
I also would support individual volume adjustments at the receiving end, as an alternative.
MH