1. Merging the doll with the doll's armoor before putting it in the box.2. Mergin either the Oscillater or electrodes with the power amp.
I think it's the power amp both found and can buy from Croc.
I am on my second run through of the game and have a gadgeteer in this party (didn't last time first party imported). This might be the way to create the two (so far) mythical entities Demon Doll and High Voltage Transformer. The reason it might be so is the Ptorch has a useful function of it's own (Light) combine it and
you get another useful device. Still hve no idea about loudspeaker and electric eye though.