Hm, are you sure thar it's distortion at the A/D point? Could it be
'popping' caused by the trombone or trumpet?
I would try to 'break-it down' a little. Do you have the same problem
with all 3 mics? Try them one by one, one instrument (or kind of
instrument) at a time. Have them play the 'loud' or 'punchy' passage
and see what's happening. Try a pop-shield as well (you never know).

Good luck,

Evangelos