You need an aftermarket HU. IMO, it's the first step in any system. I've yet to hear a decent sounding system on speaker level inputs. As far as the amp is concerned, Sony is lower end in the audio world...unfortunatley, the amp probably doesn't even put out what it's rated at. The RF (I'm assuming that's what you mean when you say "Fozgate") amp is probably better. First things first though, get an aftermarket HU and you'll hear a major difference.