I am thinking of replacing the factory stereo with a Kenwood Nav unit. It supposedly has 4x50w of power peak. Is this how the factory unit is powered? With the factory speakers (which I think sound fine) will this head unit still sound good? I am worried there is a factory amp somewhere that is seperate from the factory head unit.

 

The stock HU has settings to optimize the sound of the stock speakers. It's not to say that the Kenwood would sound bad, but you'll need to play around with it's EQ to get the sound that you like. In terms of power, both units put out about 10-15w per channel. Why not the 50w advertised by Kenwood? The key is the word "peak". the amp is giving all it's got for one burst of power, with no regard to how ragged it will sound. Notice they don't really give a distortion rating with a frequency range on peak (and there's no standard on how to measure peak from brand to brand).

There's no other amp in the car, unless you opted for the sub in the back (and that just gets an RCA level signal to it's amp). So no worries about that.