Congrats on acquiring this amp. JRDG gain adjustments are often typically controlled by jumper settings on the rear panel circuit board.
The warnings in the Model 112 user manual are pretty explicit on contacting JRDG for approval and instructions before making any changes, so for the sake of any warranty, etc., you may want to wait until you can get in contact with them.
Also, the factory setting appears to be 26dB. Did yours somehow get switched over to 32dB?