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)
Alpine PDX?
JBL MS-A series?
Zapco
Vibe Litebox
Mosconi
Suggestions?
Pavlo's
Choosing an Amp for my Setup
Amplifier wiring guide