installing new stereo/speakers advice for a 09 370z?
 

So I'm a total noob when it comes to electronics and stereos don't know much at all.

The sound in my 370 is horrible and I had these two kicker speakers laying around that I decided to use to replace the two door speakers (Kicker 43DSC504 D-Series 5.25" 200W 2-Way 4-Ohm Car Audio Coaxial Speakers) They are too small for the opening so I ordered some brackets of amazon hopefully it will fit.

Can I just replace those two speakers and leave everything as is? (OEM head unit, stock tweeters etc) or will it mess something up?

Waste of time and effort if you ask me. Do it right, do it once.

The stock HU wont even come close to making those speakers sound good.

That's what I thought, I will probably end up doing that, or maybe get a line output converter, since I kind of like the look of the stock stereo.