With Amps, if you are feeding with a signal from the HiFi coded head unit, you must use an amp that will accept balanced differential inputs
, JL is one example that will. I think Alpine PDX will also and possibly the Arc Mini.
OEM Alpine HiFi upgrade
JL Audio XD600/6 (HiFi drop-in replacement)
JL Audio XD700/5
JL Audio HD Series
Arc Mini (+clones)
JBL MS-A series?
Pavlo's Choosing an Amp for my Setup
Amplifier wiring guide