Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")
The voltage gain is going to be the square root of the impedance ratio. You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18. If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain. You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.
ok... so what do I do with all these wires?
one side, labeled "8 ohms", has red and white wires. the other, labeled "CT" (center-tapped?), has blue, black and green.
by sides I mean the diagram goes
=3||C=
I found combinations that didn't work, and some that did, but none gave me a huge boost in sound. I'm using a pair of transformers after the battery box, with just a plain signal/shield stereo pair to a 1/8 mini plug.
hope that makes sense.