Hi, I`m planning to upgrade the sound in my 2003 ML. A total makeover so to say, I have the Audio 10 cd, none bose, and no cd changer. I want to add an amp, and sub. I like the look of the interior and do not want any visible changes. Are the factory installed speakers good enough? What do you recommend if I want to replace the complete system? I hope to use the existing wiring. Iphone 5 integration is important.