I agree Mike but if he gets the sound he wants from his processor at home and can hear it through phones not garage band he will know he's sending the right sound to the mixer. and if he uses a long guitar lead and listens to the front of house mix as it goes out - and not on whatever in ear phones he is using at the moment - he'll know if the mixer and sound guy are sending the right sound to the congregation.

the real unknown as far as i can work out is how he's getting the signal to his in ear phones.- from what send on the mixer and how its being sent and whether that is the sound that's going out front.

i've tried to suggest how to eliminate likely causes by getting the right sound at home and then listening to the front of house mix as it goes out. that seems to me the only way to sort out where the problem is.

it will be interesting to see if he tries what i am suggesting.