Head unit / amp question

To begin, I am not a stereo/audio person in the least. I just traded in an 06 330i with the upgraded stereo system. That stereo sounded great. I loved it. Just bought a 2013 328i with standard stereo. I never listened to the stereo during the test drive, I "assumed" it would sound good. It does not. I plan to buy the bavsound speakers. My questions:



1 - No one seems to question the head unit. Is it fine? Same quality as HK head unit?



2 - Replacing factory amp...(again, not a stereo person)...Do you have to run all new wires to the head unit, or do you use the existing wires from the existing amp and some kind of harness. I would not replace the amp myself, just curious about how much effort is involved.



Thanks