jah..
why not do the following for simplicity//control.
do the song in biab , then after getting it right create a mp3.
put a clik at front of mp3 that only the drummer hears via his feed..
??
or if the other musicians have mic/earphone combos they will
hear it also as a monitor mix cue.
the advantage of this route is not just simplicity ..
but my concern is if the mac is playing back biab traks "live"
that any computer glitch might lead to problems/red faces all around/.
if were me i would give the 9 members each one of those mics with earpieces attached
possibly . sending em the mp3 mix. ??
do you havce some kind of PA set up at the church ??
if you have such plus a mixer one input to the mixer could be the mp3 mix
and other inputs the 9 members mics. then mix the shebang to stereo
feed for the monitors the assembly hears.
carefull use of the fader in the mixer will ensure the assembly dont hear the cue clik
at front of each song.

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