The PIC (programmable interface controller) is a chip that's used to communicate and control voltage with the ASIC chips.  Basically it's there to make sure the ASIC chips are operating at the proper voltages and for temperature monitoring.  I'm guessing this mod is used to bypass the PIC's controlling of voltage.

In the case of your missing ASICs, from Bitmain's FAQ, they call it 'chip scission'.  I believe there is an issue with the hardware around one of your ASIC chips causing the chain to be broken, I don't think this mod would be applicable in your case.