Does anyone happen to know what pots are used for the volume control at the coin door? The cab only had one in it when I got it, and it is 75ohm. There is not enough range to go from no sound(or even low sound) to nice and loud.
The pots at the coin door were only intended for balancing the two channels and making minor volume adjustments. Rather than sweeping the wiper between the + and - signals as a normal volume pot would do, they simply insert a variable resistance from 0 to 75 ohm* into the signal path. Assuming the speaker is 8 ohm, that allows for somewhere in the neighborhood of 20 dB of attenuation.
You could rewire them as regular volume controls - you'd need to make some harness modifications, and keep in mind that you're dealing with speaker-level signals, and I'm too lazy to figure out the pot values you'd need. Another option would be to remove the on-board pots, install similar value pots up front, and run wires from them to the old pot locations on the board. Or, tap the signals at the stereo / mono jumper and use a separate audio amp, putting its controls at the front.
None of those ideas are probably reasonable to implement by tomorrow, so I'd suggest turning the front pots all the way up, adjusting the board to be just a little louder than you want, and then you should be able to trim the sound appropriately with the front pot.
* - yes, I think that is the right value, but I'll be darned if I can find a confirmation of that anywhere. The pots aren't shown on any schematic I can find at the moment.