Here is my update and I must say I am pretty happy with the results. I also have the factory premium system. I replaced all speakers, except the sub.
this was good but now what I was looking for. After reading the forums I chose not to replace the head unit. I added a 5 channel Rockford...
I also have the alpine 8.4 with factory sub. Like you I wanted better sound. I had all my speakers replaced It did help but not enough in my opinion. My audio guy said that when the sound leaves the factory amp that it is stripped of most of the high and lows due to the cheap factory speakers...