ShawnSmith, yes, I did mean the music being amplified. I had read that AT831s didn't work terribly well with unamplified music, though never tried it. TheWildKindness just turned that round.
I've run several A:B comparisons between AT853 and AT831s over the last month or so, and the AT853s are just hands down better mics. Bottom end is fuller and the overall sound more rounded. I still love the sound of both, and have not put the AT831s to one side yet.