inputs.text: wow great little amp - amp running jbl p series 65 components front jbl p series 3way 6x9s back upgraded amp pdx 4100 also great little amp alpine pdx m12 subs kind wanted amps match cosmetically warn two pdx 4100 pdx f4 amps slightly different mounting hole locations also means old new pdx amps not stack amp seehems little efficient power sounds little bit cleaner warmer imaging not change tell pdx 4100 wondering worth upgrading sq benefits imo would not worth form factor amp great installation ease sq clean tuned systehem smd dd1 people seehem pair pdx f6 m12 find f4 adequate depends speakers car sounds great kinds music