2) try to pick the signal up off the audio board before the pre-amp - would have to check to see if this is possible.
Yep, you definately need to tap off the audio (line level) that is feeding 'into' the pinball amplifier.
This signal preamp signal would be 100's mV (milli-volts) upto 1volt at most, and the speaker drive output would be peaking up around 12volts (based on it running on a single 12v supply).
12v is far too much level to put into a preamp input.
If you have a diagram of your pinball soundboard, we can show you where to tap off from....
MM.
