The only non-standard aspect of the hookup is Allen's odd implementation of the expression pedals. As you probably know, each pedal contains a light source and one or more light-dependent resistors. The resistors, one per channel, are connected through capacitors to the organ's amplifier inputs. As the LDRs vary their resistance, they shunt varying amounts of signal through the capacitors to ground; the capacitor values are chosen to give a frequency-dependent expression that mimicks the action of real swell shutters.
This Rube Goldberg arrangement depends on the signal being supplied to the amplifier inputs from high-impedance sources so that the LDRs form the lower legs of voltage dividers. Normally, the signal source for the amplifiers is the digital-to-analog converter outputs from the DAC board. But when you install an HLabs device such as a reverb unit, it goes between the DAC and the amplifiers, rendering the expression ineffective because the HLabs component has a low-impedance output. The "isolators" that they sell for way too much money are nothing more than series resistors in little cans with RCA connectors. By plugging these isolators in between the HLabs outputs and the amplifier inputs, you restore the high-impedance drive and make the expression work properly.