Hi!

I'm a complete PA system novice, but I've been trying to work out how to
upgrade my church's sound system to include some volume controls. Done a lot
of reading/researching on Google, and I've got the hang of some of the
concepts. I'm hoping you guys can help me with the rest!

Currently, we have what seems to be a 100V constant voltage sound system
that's set up like this:

The amplifier (no model, no make at all, helpfully) is directly connected
to:

1) 2x 'Bouyer Type RC15' speakers.
At the back panel of these is the specifications which says that for a 100V
system:
Tap 1: 20W, 500 ohm
Tap 2: 7W, 14 ohm
Tap 3: 2.5W, 4000 ohm
I'm not sure which tap is actually in use, but I'll take a look next time I
see it.

2) A box which contains a 100V 'Line Matching Transformer', which is in turn
connected to 2 fairly ordinary hifi style speakers. This transfomer has a
number of taps, and I can't remember which one the 100V side is connected
to, but the speaker side is connected to the 4 ohm connector. I also don't
know what impedance the speakers are, but I would guess that they should be
8 ohm speakers... as they are connected in parallel...

3) An individual speaker which has another 100V 'Line Matching Transformer'
inside it, with a volume control which connects the speaker to the different
taps on the 100V side depending on where it's set.