Anything straight off the desk is not goign to give you an accurate representation of what is going on in the room - especially if it is a small room. In most rooms, but especially smaller rooms, what the congregation is hearing a mixture of noise from the stage plus what you add to it - if you record right off the desk all you are hearing is what you are adding to the mix - fine for sermons, terrible for music.
I would suggest getting a couple of good condensors , maybe hung/mounted from the roof into a 3-way balun (i assume this is what you mean by matching box - mic inputs with level control and a mini-jack output to the camera?) along with a feed from the mix.
if you get a balun with headphone capablities, get the person operating the camera to listen in and adjust the mix of desk vs room until it is just right - you might want to gt them started during sound check. If you use this method i would also suggest that during the sermon you turn off the room mics so that you get clean vocals from the desk.
if you want consistant sound you might want to mix it loud at the balun and find a way of putting in a compressor whcih mixes it back down to anacceptable level - that way when you go from music (which would be heavily compressed) to just vocals (only slightly compressed) the overall volume would be comprable and not significantly quieter.
This is only theory/thought from a guy who works on both video and audio in the pro and church arenas - i haven't actually tried it, so if you can borrow the gear, give it a go before you invest.
