According to Alpine's user manual for the MRV-M500, it mentions nothing about differential balanced inputs. It only mentions pre-amp level inputs or high-level speaker inputs. If the amp is working with the premium head unit with a direct connection, maybe it does accept the differential balanced inputs from the head unit. If you hop over to Crutchfield and look at the JL Audio 5-channel amps and the Infinity Kappa Five, they specifically mention differential balanced inputs for connection to virtually any car stereo head unit, including factory head units. That is why I chose the JL Audio amp because I knew it would be compatible with the Honda premium head unit. The Honda wiring diagram for the premium head unit and amp identify the outputs as pre-amp level outputs. I learned about the differential balanced outputs from Driveaccord.net, in which the 8th generation Accords with premium sound were using differential balanced outputs. The Civic wiring was similar, so I knew the Premium system in the Civic was also a differential balanced system. The shop used the wiring diagrams in my original post to install the JL Amp, speakers and sub.