Features that, all in all, are not uncommon in the marketplace. I was hoping you would ask that question. First, the EPX preamp has special input circuitry. In car audio, most components are connected together with RCA patch cables. Under ideal circumstances, the difference between the hot lead and the outer shield conductor is the musical signal.
Cars are anything but ideal, however.
Electrical noise is generated by the alternator, fan motors, windshield wipers, brake lights, and who knows what else. These noises can be inductively coupled into the RCA patch cables. When this occurs, the noise spikes appear on BOTH the center conductor and it's outer shield. Since differential input circuitry amplifies only the difference between the two conductors, the noise spikes are NOT amplified, and they are consequently eliminated from the system. To further reduce the possibility of noise, each set of RCA inputs has it's OWN independent audio ground.