run your mics with the BB and into the line in jack.when the music starts set your levels manually,max out the meter at about 3/4 of the way.you wont have any problems.
also.before the music starts go into the menu and set the controls over to manual,then go into pause mode.this way when the music starts the setting will already be adjusted and all you have to do is hit unpause,and then make you level adjustment as needed(most of the shows i do around "24/25" on the meter works fine.
i think the amp on the mic jack is only like 3 or 4 volts,this can only handle very soft acoustic music,any hard/louder music will brickwall everytime.
always use a BB.you dont want to suck precious juice from the recorder,and if you have a r/o on the BB you'll want to utilize that as well.